Category Archives: Weapons Technology

You Don’t Think of “Beautiful” When You Hear “Skeletal.” You Should.

skeletal doubleWe like to pride ourselves on our gun knowledge, but we know there are things that we don’t know at all well. Some of these things we know we don’t know, like fine double sporting shotguns. (The scary bit is, as Don Rumsfeld knew, not the stuff you know that you don’t know, but the stuff that you don’t even know that you don’t know).

But when we look at a beauty like the Hugh Snowie/Thomas Horsley on the right (which you really must embiggen), we want to know more. Fortunately there’s an article by Douglas Tate in Shooting Sportsman: The Magazine of Wingshooting and Fine Guns that assumes you know nothing, teaches you the basics, and leaves you wanting to know more.

Before we dive into the article, take a good look at that beautiful Snowie piece. What looks like the side lockplates of a percussion fowling-piece are actually protrusions of a receiver that is so cunningly inletted into the fine French walnut stock that it looks like several pieces, when it is really only one perfectly-shaped one. The quality of the materials and work are staggering, which is par for the course in the examples that Tate shows in his article. (The pictures come in the case of current guns from the makers, who take a justifiable pride in these works of art; and in the case of vintage guns, from the auctioneers who handle these fine-art firearms).

Bar-in-wood shotguns owe their graceful good looks to their parents: They are the direct descendents of muzzleloaders and can be defined as breechloaders in which the lockplate or action body and sometimes even the knuckle and hinge pin are enclosed in a forward extension of the walnut buttstock. They come in hammer, hammerless, round-action and even bogus boxlock configurations known as “body locks” and have become desirable collectors’ items.

According to Gavin Gardiner, who has worked with Sotheby’s gun auctions since 1987, “Bar-in-wood guns were a way of maintaining the gracefulness of a muzzleloader in the early breechloading era, but the easier-to-make and stronger designs soon cast them into the shadows.”

“Pretty much all makers made them—certainly the better-quality ones, anyway. It is just that not many of them continued to make them for long. Westley Richards, Purdey and Horsley are the three that jump to mind as makers that produced good numbers, and of course we have MacNaughton, with their bar-in-wood Edinburgh-actioned hammerless gun. MacNaughton is probably the only one who has made a modern version, though I am sure if you ask, others might.”

MacNaughton is one of the last firms to make them, but it was also one of the first. In July 1867, James MacNaughton registered improvements to a slide-forward-and-drop-down hammergun that was “applicable to the conversion of muzzle-loaders into breech-loaders.” The patent illustration and surviving examples feature wood-covered actions. Common enough in the 1870s, timber-shrouded actions were felled by stronger competition. The few hammerless sidelock ejector examples surviving from beyond this era are some of the most coveted wood-covered actions.

via Skeletals in the Closet – Shooting Sportsman.

Tate goes on to describe the different types and makers of double “bar-in-wood” or “skeletal” guns, with a few illustrations to whet the appetite (and links to the makers). Of course, these guns, painstakingly handcrafted by Old World craftsmen, are not priced for the middle-class upland hunter. But anyone can look and admire them. It’s a good respite from looking at utilitarian M4s and sewer-pipe STENs, you know?

bar-wood-pairWe showed an example of Philipp Ollendorff’s work, which we learnt of from this article, in a previous Friday Tour d’Horizon post here, but we think you will enjoy the article, even if, like us, you’re not much of a hunter and your taste in shotguns runs more to a Winchester M12 riot gun or a beater no-name boat gun or breaching tool.

We’ll leave you with the brace of James McNaughton doubles on the left. We are not sure if royalty still hunts birds any more, but if you do hunt birds and want to feel like royalty, well, the kids can earn scholarships (or go to the Military or Navy Academies) if you blow their college fund on their heirlooms instead, yes?

A man after our own heart (but, alas, probably with better taste), Mr Tate closes his article with links to the two surviving bar-in-wood/skeletal gun makers, Dickson (who makes McNaughtons these days, also) for the classic Scots gun, and our previously linked Ollendorff for the Mitteleuropaïsch variety — both of which make guns of admirable beauty.

Author’s Note: For more information on bar-in-wood guns, contact Philipp Ollendorff,; or John Dickson & Son,

Hey, your kid’s gonna learn more in Hard Knocks U anyway, you know it.

Snap, Crackle, and Pop

Well-known (and respected) trainer Kyle Defoor was conducting training at for a military unit when one of the unit’s long guns went down, due to this:

defoor bolt failure

Yes, that’s an AR/M16/M4 bolt with a single lug fully failed. Possible causes for the failure include (at a fundamental level) manufacturing error, corrosion or fatigue. It’s hard to judge from this hole, but going way out on a limb, it looks like there’s a somewhat granular failure at the left end of the fracture, with a smoother “sudden” fracture face on the right end nearer the extractor, presumably because the fatigue failure left too little of the remaining metal to bear the stress of firing locked in battery, and the remainder of the part failed from the crack due to overstress. But it could also be caused by swapping a fresh bolt into a gun with a worn barrel extension (or vice versa) in the field, so that only one lug was bearing all the tension of locking — result, failure. Or the gun may simply have been made without the locking lugs all engaging properly — it’s happened before.

A gun with a failure like this may or may not continue to fire for a while. But if overstress on one lug was a factor, the loads formerly too much for seven lugs now bear upon six — it would not be wise to bet your life on this firearm.

Kyle, though, had another issue with the failure — and the unit whose arms room coughed up the firearm that did it.

On 9 July, he posted this image to his Facebook feed, saying:

Maybe I should start to amend contracts to include an armorer and spare parts?

With a hilarious set of hastags including, but not limited to:

#‎takecareofgear‬ ‪#‎ittakescareofyou‬ ‪

…and the snark-infused:

‬ ‪#‎logisticswinswars‬ ‪#‎waistingtrainingtime‬ ‪#‎youdontpaymetoplumb‬

The part was, as you can see from the markings, a factory Colt, magnetic particle inspected, bolt (or a counterfeit thereof that somehow got into the supply system — not impossible). It had unknown hours and rounds, because Big Green is not in the habit of keeping meaningful usage and maintenance records on small arms.

Apart from spelling “wasting” wrong, there is not much to argue with in Defoor’s response. Apparently the unit in question did not provide an armorer for the range event. In most units, the armorer doubles as a supply clerk and is not thought of as necessary for a range evolution (except to manage draw and turn-in of weapons at the Arms Room). In addition, the Army has been working to reduce the number and kind of spare parts available at organizational level. This is due to politically anti-gun policies, and Army civilian political appointees who believe (however lacking the evidence may be) that Army stocks are a significant source of crime guns.

Even if the parts were by some miracle on hand, the standard Army armorer, one each, is neither trained nor authorized to replace a failed bolt. Armorers given scant and cursory training on maintenance.  Instead, their course, an add-on for supply clerks, concentrates very extensively on paperwork, records-keeping, and the process of appearing to be conducting scheduled maintenance. This is also borne out by what actual combat units and their commanders value, based on how they judge and critique their armorers. No one is ever graded on the only maintenance measure that ought to count, the combat serviceability of the unit’s firearms; everyone is constantly graded on the process, on the appearance of maintenance, and on maintenance busy work. While we’d bet nine out of ten of the readers of this blog could fix this rifle in minutes, the only thing a company, battalion or even brigade armorer can do with it is turn it in.

Military maintenance bureaucracy does all it can to limit effective maintenance of small-unit equipment, notably including small arms, optics, and radios. Problems with these are most effectively solved by trained, experienced personnel at the lowest organizational level, so naturally such personnel are just flat not available.

Instead, you must tag the weapon or other piece of equipment down. Naturally, there are different rules for weapons and weapons equipment, vehicles, radios, and special weapons (i.e. WMD-related stuff), although the Army does try to squeeze them all onto standard forms (DA-2404 for regular maintenance, DA-2407 for turn in, nowadays it’s an electronic form, DA-2407E, done in the SAMS logistics computer system).

The weapon can’t be sent directly to the level that can fix it, even when (like this) the level is obvious and the weapon could be inspected and classified by a well-coached Helen Keller. It must go up the operator-organizational-direct-depot support chain, getting a new inspection at each

Plus, while the weapon is turned in, what is Joe Snuffy supposed to shoot? No Army unit maintains operational floats or spares (unless it is, by happenstance, or the customary incompetence of all Army personnel managers and activities, understrength). So Joe will get the weapon of whoever is on sick call or leave when the unit goes to a range, unless it’s one of the very large number of units that does an absolutely crap job of tracking who is assigned each particular weapon, in which case it’s musical chairs and the last one that shows up gets a new weapon.

The Army actually tries to bill giving a guy a new rifle for every annual, semiannual or quarterly trip to the range as a plus, believe it or not: “Everybody gets valuable experience in zeroing.” (Meanwhile, of course, everyone loses confidence in the ability of his gun to hold zero).

It does not help that the standard M12 rack does not accept a rifle with optics. In the Arms Room, it’s still 1988.

Moreover, the Army’s weapons records are a chaotic mess of rack numbers, serial numbers, weapons cards, hand receipts, pencil sheets, green-and-white property book printouts (that may not put all your unit’s rifles, for example, together on the same pages), and unofficial Excel-spreadsheets and Access databases, which interface more or less (mostly, less) with one another and with the unit’s personnel assignments. This means that every time you cross-level personnel from 2nd platoon to 3rd platoon, if your arms room is nicely organized by platoons, Joe Rifleman is going to get a new rifle and be off zero until next range trip, and so is Bill Bulletician who’s coming from somewhere else… that’s another reason why no Army unit beyond the Ranger battalions and the 82nd Division Ready Battalion actually dares to ship out to combat without a trip to the zero range.

In addition to the deployment delays that come because no one has confidence in his optic zero right now, we also endure a colossal waste of time because weapons inventories are unnecessarily hard. (One of the nice things about HK 416s? Their serial numbers are highlighted. Seems like a small thing, until you’ve tried to inventory a couple hundred M16A2s by the light of a flickering fluorescent bulb that there’s no budget to replace. And if you highlight the number with paint or permanent marker, you can actually get dinged on inspection). Every arms room needs to be inventoried periodically by senior personnel who have better things to do, and many aperiodic inventories are demanded by regulations. The faster these go, the better for everyone, but the Army has a settled way of doing things that proceeds from the assumption that the net value of a soldier, NCO or officer’s time is always zero.


Testing Polymer Receivers to Destruction: Factory and Printed

Here’s another embedded video from’s InRange TV, where Ian and Karl do their level best to destroy a Cav Arms polymer lower.

They step on it, stomp on it, run it over with a Jeep, and shoot holes in it, and still it keeps on shooting. One is reminded of the old Timex ads, “Takes a licking and keeps on ticking.” Maybe it should be “Takes a drilling and it keeps on killing (IPSC targets).”

We’re not really shocked by this. We had AKs and SKSes in the foreign weapons arms room in 10th Group that were Vietnam captures, complete with bullet and claymore holes, and they all worked. (We kind of doubt their previous owner Mr Nguyen was still in such adequate operating condition). And we’ve seen ARs take some pretty brutal treatment and keep on shooting, including carbines that would still chamber rounds after their plastic was all burned off and their magazines blown out by a helicopter post-crash fire (we didn’t shoot them, though), and an M16A1 that still functioned (albeit inaccurately) with the barrel bent 30º off axis at the FSB1 (it was under a trooper’s armpit when he executed a really craptacular PLF2, dislocating his arm and bending the rifle).

A really good design is overwrought enough that it can be degraded by wear, corrosion, or, yes, combat, a good bit before it fails to function. And a really outstanding design delivers that with the smallest weight and bulk penalty possible.

Cav Arms made quite a few of these lowers out of durable Nylon 6 before the company was singled out for destruction by the ATF, which is a long story and off this topic. (A seemingly complete technical history of the Cav Arms lower has been prepared by Russel Phagan, aka Sinistral Rifleman, who assisted in the video). A successor manufactures the lowers today. (But the most significant thing about the lower wasn’t the company’s grim fate; it was that the lower was redesigned from the ground up to be made of polymer, to take advantage of this material’s strengths, and to shore up its weaknesses).

As Ian points out towards the end of the video, a polymer lower designed to be a polymer lower is a better bet than one that is just a molding of the traditional 7075 alloy machined forging. (Conversely, a steel receiver that follows the form factor of the alloy lower is going to be overstrength and overweight). These follow from the differences in the strengths of the three materials.

Ian notes the weakness of the buffer tower if the normal lower receiver is modeled in anything other than metal, and that gibes with the results that early lower-receiver 3D printers had, substituting much weaker ABS or PLA material for the 7075. The first point of failure to be made manifest was the buffer tower area. This led to reinforced buffer towers and ultimately such heavily-reinforced lower-receiver designs as the modern Aliamanu-Phobos.


Along with the reinforcements named in that slide, the massively reinforced buffer tower is evident. But even this beefy design can fail. This one started to delaminate with just 20 rounds fired. Test firing the lower:

trouble1 aliamanu-phobosHere’s the first image of the delamination. Since all the fire control group parts are above the delamination line, the weapon should still operate, but this obviously bodes ill for any probability of it surviving further testing. (Yes, these do embiggen for more of a close-up look).

trouble1 delamination 1Here’s the other side at that 20-round point:

trouble1 delamination 2


Firing more rounds just cause more failure, in this case it seems that the area around the grip screw also began to delaminate, releasing the grip:

trouble1 delamination 3At this point, stick a fork in it, it’s done.

Others have had much better results, including from pretty low end perimeters, and the equipment and parameters that FOSSCAD member trouble1 used didn’t seem out of step with what the successful printers did. But you can’t call this a successful print. It seems highly probable that there is some failure in the print setup or materials (moisture in the filament?) that no one has figured out yet.

That delamination is an interesting failure mode that’s fairly common in fused filament fabrication printing, is only one reason the technology is not yet ready to compete head-to-head with plastic injection molding. The much slower production of the additive process, and its higher per-unit variable cost, also argue against this for production. However, injection molding, with its generally higher fixed costs (for tooling), is unsuitable for prototyping and very short production runs. A hybrid of technologies that uses printed molds to reduce that fixed cost for short runs offers the potential of closing the gap. But a proper part is a part that is designed in conjunction with its manufacturing technology — engineered for production from Day One, with materials  chosen to meet the mission and simplify, speed up, and save money on production.

As Ian noted about the Cav Arms polymer lower (which is injection molded), it’s necessary to design the part to make best use of the materials and technology. Simply trying to reverse-engineer a popular firearm in a new material or manufacturing approach will only take you so far. It may, given enough iterations, be far enough.


  1. FSB = Front Sight Base, the triangular-shaped forging that holds up the front sight on the nose of AR-15 series rifles through the early M4A1. It also locates the gas tube and hosts the bayonet lug — a busy small part.
  2. PLF = Parachute Landing Fall, a specific roll that reduces the risk of injury when a para touches down.

Wednesday Weapons Website of the Week:

We think we know our way around guns and gun history, but in fact we know, mostly, the success stories — the winners that went forward into widespread use, more than the many other ways that were tried and found wanting. This Civil War veteran revolver is one of those also-rans; can you identify it?


It’s a French Lefaucheux pinfire revolver, in 12mm pinfire (about .47), introduced in 1854 and so edging Rollin White’s .22 short Smith & Wesson by a bit. Pinfire had some pros and cons. The rounds contained a primer or cap internally, including an anvil and a priming mixture, and the cartridge held a pin poised above that cap. The firearm’s hammer drove the pin into the anvil, setting off the primer and the (black) powder. Contrary to common belief, some pinfire rounds, at least, were field-reloadable. Both the Union and the Confederacy bought Lefaucheux pistols, and they were also very common as private-purchase arms for European officers before the centerfire system’s dominance was fully established.

They persisted for a very long time; Gustloff-Hirtenberg in Austria made pinfire ammunition as late as 1944 (stopping just before, or as soon as, the Red Army rolled over the plant), suggesting that the 90-year-old revolvers were still in second- or third-line service somewhere in Mitteleuropa. If the Soviets did their usual thing and carted the machinery off as reparations without checking it, they were probably pretty sore when they opened the crates and found out what they’d shipped. Needless to say, they never restarted production.

An education in pinfire and other alternative early ignition systems can be had at this weeks Wednesday Weapons Website of the Week, which is called the Cartridge Freedom Act (or by its URL, but it’s basically the blog and webpage of advanced early cartridge collector and historian Aaron Newcomer. Aaron freely shares his knowledge, his expertise, and his articles for cartridge collector magazines, demonstrating a deep knowledge and fresh enthusiasm for these time capsules from the dawn of the fixed-ammunition era.

In the early days of cartridges, today’s center- and rimfire rounds were far from the only ideas tried; they’re just the only ideas that still survive today. Indeed, it wasn’t at the time completely obvious that they would be the winners, and early centerfire cartridges tended to have some differences from those today (we keep meaning to do a post on early balloon head cartridges, whose manufacture had a lot in common with rimfire cartridges of the day).

Here’s another dead branch on the evolutionary tree, cupfire cartridges. These were like a rimfire cartridge, except the “rim” was in the front of these front-loaded revolver cartridges, and the hammer struck the cup in the rear, which contained the priming mixture, against the side of the chamber. This was a dodge to get around the Rollin White patent on through-bored cylinders loaded from the rear. The cartridges are a .28, three .30s, and a .42 — even the dimensional nomenclature of these oddball rounds was different. They were popular enough to be loaded by several ammunition producers, despite being utterly forgotten — except by Aaron and other collectors, perhaps — today.

cupfire7 An advantage of cupfire was shared with center- and rim-fire: it didn’t matter how the cartridge was oriented. For a pinfire round, naturally, it mattered greatly, but there was usually a notch to make sure the pin went in the “right” way. Some time on the site will make you smarter about this kind of thing.

We were drawn to the blog when we read this thread on Reddit, and were originally going to simply blog the subject of the thread, the rare .58 Schubarth round, so rare in fact that a note card from a previous owner, Berkeley R. Lewis, Colonel, Ordnance, misstates that it is a Gallagher and Gladding round. It’s amazing that Newcomer gets this right when Lewis had it wrong. (The Schubarth patent was different from that of Gallagher & Gladding).

lewis noteThe rifle was a complicated conversion of the Springfield. Looking at this drawing, it’s easy to see how the far simpler centerfire Allin conversion (which also didn’t have any right way or wrong way to load the rounds) won out.


The rounds were reloadable with Minié balls and, we believe, ordinary percussion caps. Here’s a picture of the egg-shaped, 2-inch-long loaded cartridge:


Aaron’s post on the .58 Schubarth has more pictures, including those of other rare specimens (including a fired case) of this near-unicorn rarity, from the collections of his friends and fellow collectors, and patent pictures. He’s also been answering questions in the Reddit thread.

We were meaning just to blog the .58 Schubarth, but then Nathaniel F at The Firearms Blog did, and since a lot of you read that site too, we took our post in a different direction.

Bonus thing to find on his page: there’s some really interesting stuff on excavated Civil War pinfire casings.

While the Civil War has a reputation as a muzzle-loading war, cartridge arms were coming into vogue, and by war’s end Union cavalry were predominantly equipped with breechloaders, mostly rim- and center-fire single shots, but also some repeaters.


Do We Need A Bigger Bullet?

Jim Schatz, former HK USA manager (during the period of peak Because-You-Suck-And-We-Hate-You customer service, actually) always has one of the most interesting presentations when he’s up at an NDIA1 conference. The slides from this years’ NDIA are up (here), and Jim’s presentation, interesting as ever, is up here (.pdf). Jim wants us launching bigger bullets, to longer ranges.

Jim’s basic beef is probably best encapsulated in this quote from an SF team sergeant:

Few enemies would even consider taking America on in a naval, air or tank battle but every bad actor with an AK will engage with U.S. forces without even a second thought.

To boil down his argument to a single-sentence thesis: The US lacks small-arms overmatch, and only changing cartridges can get it for us. He defines overmatch by effective range. As he sees it, this is what the world looks like today:


As a former infantryman, Jim knows that weapons don’t square off one-against-one. On the battlefield, units from corps to squad size all maneuver to bring their organic, attached and support firepower to bear on the enemy (who is doing the same, inversely). It’s a common fallacy that (for example) because every squad in the Ruritanian army has a designated marksman, our squads should have one too. (Maybe they should, but not directly because of what the Ruritanians are doing). As you can see, Jim’s focus on range leads him to pair off sniper rifles with light machine guns, weapons which have similar effective ranges for completely different reasons, even when they fire dimensionally identical ammo.

As far as his 1000m effective range of the SVD is concerned… he must have shot one?

Here is one of his proposals for overmatch. There’s a few things screwy here (the SVD has grown  an even-more-ludicrous 500m of range, to 1500m), but that’s not important. What is important is the argument that going to an Intermediate Caliber Cartridge (something like the 6.5 or 6.8 or something all new in the 6-7mm neighborhood) for rifles and to .338 for support weapons will provide significant range overmatch.


The increased ammo weight can be made up in part by polymer or semi-polymer (i.e. with a metallic base) cases.

Jim at least partially neutralizes the cost-in-times-of-drawdown argument by suggesting that the new weapons go only to the tip of the spear, the guys whose mission it is to produce casualties, and take and hold ground, with these weapons. That’s only about 140k actual shooters out of the much larger service. A finance clerk needs a rifle, sure, but he or she can live with the latest-but-one.

Bear in mind that the target set is also not static, while we’re developing all these new weapons the Russians, the Chinese, and even the ragtag insurgents of the world (who have definitely, like Russia, pushed more 7.62mm weapons down to squad-equivalent level than heretofore) are acting, adapting, and changing, too. We don’t need to overmatch the enemy today with the weapons we’ll have in ten years. We need to overmatch the set of weapons the enemy will have ten years from now, in ten years.

Men can disagree about how best to get there. Assuming we stick with the M16/M4 platform, Our Traveling Reporter would have us go to the 6.8 x 43. (It was news to him that the Saudi Royal Guard has adopted this platform, in LWRC carbines, or that military 6.8 is in production for export now by Federal — formerly ATK). We would probably go with the 6.5 (x38, although the length designator is seldom spoken aloud) Grendel for its lower BC and higher sectional density (=longer effective range, flatter trajectory, more energy on target). The 90 grain Federal load in the 6.8 is very effective closer in (the 6.8 was developed with SF input as a CQB cartridge).

Some current contenders --  M855A1 5.56; 6.5 Grendel; 6.8 SPC; 7.62 NATO. From an excellent article by Anthony Williams setting out the historical context.

Some current contenders — M855A1 5.56; 6.5 Grendel; 6.8 SPC; 7.62 NATO. From an excellent article by Anthony Williams setting out assault rifle ammo in historical context, including many old, obscure, and outright forgotten attempts. Shape of the 6.5 suggests a superior BC. The 6.8 is compromised by its 5.56 ancestry and packaging (bolt head size/overall length).

This is not an entirely new or novel idea. As mentioned in the caption to the photo above, British researcher Anthony Williams has a very fine article on Assault Rifle History with lots and lots of ammunition comparison photos. Back in the 1970s, a guy whose business was called Old Sarge, based in the highway intersection of Lytle, Texas, made a quantity of 6 x 45 guns and uppers. Based closely on the 5.56, these guns (most of them were built as what we’d now call carbines) were completely conventional, but like today’s 6.8 SPC the intent was to create superior terminal ballistics. We don’t know what happened to him or what seemed to be, when we stopped in, his one-man business (he talked us out of a mod he’d done for others, an M60 bipod on an XM177).

If we have a serious criticism of Schatz’s work here, it’s that its focus solely on range as an indicator of overmatch understates the problem. Hadji with his AK and mandress has a lack of fear of our troops that stems only partly from his belief that range makes him safe (and only partly from his paradise-bound indifference to being safe). His feeling of impunity stems from a belief he won’t be engaged at all, won’t be hit if engaged, and won’t be killed or suffer significantly if hit. We need to increase the certainty that our guys will fire back, not just increase our pH, and we need to increase our pK as well. The first of these is far outside the scope of weapons and ammunition design, but it is, in our view, the most serious shortfall of US and Allied forces.

We have another beef that’s not specific to this, but that arise with any attempt to pursue range or other small-arms overmatch: it never works. There are only two ways pursuit of overmatch can finish. Either your new weapon does not constitute an overwhelming advantage, or it does — in which case everybody copies it most ricky-tick. Mikhail Kalashnikov died bothered by the fact that he never got royalties on any of the millions and millions of AKs made outside of his homeland, but the guys who really got copied were the engineers who built the StG.44. (True, the AK was better adapted to Soviet expectations, traditions, manufacturing capabilities, and training modes, but it was certainly inspired, conceptually, by the first assault rifle). It was a good idea. It was exclusive to Germany for mere months (of course, that they were losing the war may be a factor, but that the war ended was certainly a factor in slowing the adoption of assault rifles in Russia (a little) and the West (a lot).

In all seriousness, if you look at the history of firearms, you see a punctuated equilibrium. For centuries the flintlock is the infantry weapon, then the percussion lock sweeps the flints away in a period of 30 years or so (faster for major powers, or anybody actively at war). Then the breechloader dethrones the percussion rifle-musket in a couple of decades… to itself be overthrown by repeaters in 10 to 20 years. Calibers go from 11-13 mm to 7-8 mm to 5-6 mm at the same time all over the world. We’ve had a very long period now of equilibrium around the SCHV (Small Caliber, High Velocity) concept. Is it time for that equilibrium to be punctuated? Schatz says yes.


  1. NDIA: National Defense Industrial Association, a trade and lobbying group for defense contractors. Formerly the American Defense Preparedness Association (when Your Humble Blogger was a member, and they were fighting a rear-guard action to preserve a defense industrial base during the Clinton disarmament/drawdown cycle), and before that the Ordnance Association.


Daniau, Emeric. Toward a 600 M Lightweight General Purpose Cartridge. September 2014. Retrieved from: ; this is a uniquely French view of this same challenge, hosted online by Anthony Williams.

Schatz, Jim. Where to Now? 3 June 2015. Retrieved from:

Williams, Anthony. Assault Rifles and Ammunition: History and Prospects. Nov 2014. Retrieved from:

Williams, Anthony. The Case for a General-Purpose Rifle and Machine Gun Cartridge (GPC). Nov 2014. Retrieved from: ; an earlier version was presented at NDIA in 2010:

(Note that Williams’s work on this matter was sponsored by H&K, a fact that is not invariably disclosed in all documents but that Williams publicly discloses on his website).


GunLab’s Reverse Engineering

We haven’t been over there ( in a while, and Chuck is always up to something cool. Recently he had something nice to say about us, in a longer post on reverse-engineering; to be explicit, reverse-engineering the MP44 trunnion. But forget what he says about, how cool is it to be making an MP.44 trunnion for (almost) the first time since a T-34 did a pivot turn on the ruins of the factory?

MP44 reverse-engineered trunnions

Here at Gun Lab we do a fair amount of reverse engineering, most of what we like to make have no drawings. However when there are drawings or solid models available we will use them. With this said I have found that most of what is available on the internet or in books is just not correct.

A case in point is the MP-44 trunnion. I have all the drawings that I have been able to find on this part, a number of different sets are out there, and when compared with the actual part have found them to be lacking. Some are just wrong and in some cases I don’t think the person has actually looked at a part.

Now, we have a set of MP.44 drawings here. We’ve actually been meaning to show a few of them to illustrate how MP.44 design features migrated into the AR-10 and thence to all its descendants. They’re terribly reproduced, no longer to scale, but they are dimensioned MP.44 drawings.

Say “Thank you,” class:


Now, you might wonder how it can be possible with apparently original (even if lousy), dimensioned drawings, you can’t just poke the numbers in and try to run the part. There are a number of reasons that you could expect drawings to diverge from shop practice. In the real world, in fact, it’s a constant battle to keep the drawings and the processes both aligned properly on the same part. In the 20th Century this got particularly bad because of engineer/draftsman/master machinist/machine operator job specialization and social stratification. Those could be four different guys whose only workshop interactions were with the adjacent guy in the org chart, and whose contacts were all correct.

There’s no way you produce stuff efficiently without the engineers going out on the shop floor, but some are loath to do that, and some shop staff are loath to have an engineer looking over their shoulders. There’s no way you produce stuff efficiently without a steel-cutter being able to walk back into the engineering spaces with a part and a problem, right to the guy who drew the drawings — but that is forbidden more often than it is allowed! So even in the best, cleanest, and least disrupted shops, lines got crossed, things fell apart, the center did not hold… wait, we got carried away there for a bit. But communications were imperfect, even in a perfect factory.

Then, add into the mix, we’re talking about the Third Reich in 1944-45. If the Germans had perfect factories, the Allies bombed them. Meanwhile, the gaping maw of the Eastern Front demanded endless human sacrifices, and in each successive draft call manufacturers could protect fewer and fewer key workers. The “fix” the government proposed for this was that they would provide labor, but that labor was at best displaced refugees from the ill-fated German settlements in the East, but more commonly slave labor from occupied nations.

Something had to go, and one of the things that went was correcting and updating drawings. Seriously, if you compare surviving German drawings to the M1 drawings, your mental picture of “German efficiency” will never recover. (Well, maybe a little when you realize that two large air forces were gamely trying to reduce German industry to the state of the Germans’ forebears in the Neander valley).

Now back to the MP-44 trunnion. We were contracted a while back with making a limited number of new trunnions for the MP-44. He sent us a very good original one and we had a poor copy of one at the shop. Using these two pieces we started the project of reverse engineering it. The easiest thing to do was look for engineer drawings off the web. These are the ones that I found.

His look like they’re from the same set we’ve got here. He has stripped them of dimensions, perhaps because he’s not working with SI (metric) dimensions, but more likely because the dimensions were not “on” compared to the physical parts he had to measure.

The measurements have been removed from these copies, however you can find them on the internet. I did use the basic drawing as a starting point. The sheets were cleaned and measurements were taken using a cmm, micrometers and pin gauges. Tolerances were set using not only the trunnion but also matching parts. When there was a doubt other parts were located to increase the measurement standards. This allowed us to come up with a reasonable solid model that we felt was accurate enough to start programing.

A CMM is a coordinate measuring machine. Think of it as a sort of 3D scanner that touches off against a part and records that position in 3D space. These can be used to gather a cloud of points, or more efficiently, to capture key dimensions.

The problem with using a CMM against a part you are re-engineering is that you’re working off one part, and you don’t know where in the tolerances that part was. (That’s also our beef with David Findlay’s excellent Firearms Anatomy books — for practical reasons, Findlay worked off a single sample of the firearm).

Given enough parts to measure, you can develop a degree of statistical certainty about where the original measurement was supposed to be. Working with most non-US products, you can also cheat a bit by knowing that engineers like to spec things in fairly round millimetric measures — dimensions that end in X.0 or X.5 millimeters, most of the time.

Anyway, here is the first post on re-engineering the MP.44 trunnion, and here is a follow-up post (in which the model turns out to need some improvement). Meanwhile lots of work improving the shop and working on GunLab’s other projects, such as the VG1-5 limited production run.

Note on an Unpleasant Subject

Technical posts like this and GunLab’s would be banned under a gag order slipped into the Federal Register by the State Department — yes, the very people who negotiated the deal to accelerate the nuclear armament of the hostage-taking terror state of Iran this week. The deadline for comments is 3rd August. As we previously wrote (more background there, at the end of a barrel-heating post):

Comments go here at or by email to: DDTCPublicComments@state.govwith the subject: “ITAR Amendment—Revisions to Definitions; Data Transmission and Storage”. Ceteris paribus, this link should open in your email application with the correct subject header.

Again, there’s more at that previous post on how to comment, but at this time it’s crucial that you comment. A State Department than can censor the Internet is a State Department that has lost touch with America.

Explained: Why The Army’s Guns Wear Out, and Yours Don’t

So the Army has a handgun problem, so they say. The Beretta M9 works OK (and we have yet to hear a complaint of any kind against the issue SIG M11 or 226/Mk 25, except the usual but-I-like-thatbetter bitching that troops always do). But after 30 years the Berettas wear out (gee, who saw that coming?)


Explained: Why the Army’s Guns Wear Out, and Yours Don’t

You might wonder why the Army managed to make the Berettas wear out, when yours is still going strong and it’s the same age. There are several reasons Army guns die younger than they really ought to.

  • First: They’re Everybody’s, and Nobody’s. Consider this: nobody ever washed a rent-a-car. Nobody takes care of someone else’s property, especially communal property, like he takes care of personal property. Service pistols are rode hard and put away wet, in a communal arms room where they’re inspected and maintained as someone’s extra duty. Remember how diligent you were about extra duties? Us neither.
  • Second: Too Much Fingergepoken. Back in the days when the old, air-cooled, inspired-by-Adolf-hisownself VW Beetle was actually a cultural  thing, you could get these stickers in German Fraktur script for your dash (we are not making this up):

Das Maschine is nicht fur gefingerpoken und mittengrabben.  Ist easy schnappen der Springwerk, blowenfusen und corkenpoppen mit spitzensparken.  Ist nicht fur gewerken by das Dummkopfen.  Das
Rubbernecken Sightseeren keepen hands in das Pockets.  Relaxen und vatchen das blinkenlights!

Like most things in VW’s small world at the time (1960s), it didn’t take itself terribly seriously. (Applied by a VW owner, that sticker was ironic. Applied by a Porsche owner, it had all the good-natured humor of a drumhead tribunal in a Womyn’s Studies Department, and was a serious admonition).

What this means in the gun world is that pistols are seldom shot, but they’re frequently carried and subjected to extremely frequent (relative to their firing) disassembly and assembly, giving them unpredictably weird wear, damage, and parts-loss patterns. We’re not really sure why the service stresses mechanical training on pistols so much, but it’s probably because they can, and there’s no immediate costs, unlike actually shooting the things, which makes you burn your ammo budget.


This is not the Army of 1940 any more, where almost everybody was a guy who grew up on a farm and could fix nearly anything. Most of today’s soldiers grew up in the city and, having been told all their lives that there are No User Serviceable Parts Inside, have come to believe it. A surprising number of Army small arms die, or at least have to be sent for third or higher echelon maintenance, because of gefingerpoken.

When we’re done laughing at the Army, any of you guys ever work as gunsmiths, or just in a gun shop? Ever have a dude (it’s always a male, 100%) with a sheepish look and a furtive manner come in with a brown paper bag of gun parts, as if he was a wino with a bottle of Ripple in there? We have heard of soldiers who did that with M9s they detail-stripped and couldn’t get back together (which is pretty pitiful, but it really happens. Ask the desk guys at Jim’s in Fayetteville).

Alternatives to brown-bagging it to the gunsmith include finding your 18B buddy to reassemble it, finding your 18B-wannabe buddy ditto, or, if it’s a privately owned weapon, just leaving it in the brown bag until your heirs sell it as a Gunsmith Special on GunBroker.

  • Third: High Round Counts. Some guns only get shot a lot. If pistol BZ60124489 gets assigned to be the armory of the divisional finance battalion, It may get taken out and shot for forty to a hundred rounds a year — or it may not. If it winds up as training pistol at a training site, or winds up in certain units that do a lot of live fire, it can fire 4,000 rounds a year. There are actually parts that have a round-limited life, but:
  • Fourth: Undocumented use and maintenance. The Army does a lousy job tracking the use of its firearms. There are three basic ways of knowing when to replace machinery: you can overhaul on calendar, assigning a pistol (or car, or airplane propeller hub, or anything) ten, or thirty, years of useful life. That means that some will break before getting potentially life-extending maintenance or being replaced, and some will get maintenance or replacement they don’t need, but it’s one way to do it. You can overhaul on use, but that requires you to (1) set a use metric, which will have the same problems of under-over as a calendar metric, and (2) to track it diligently, which fails in the Army because it’s no one’s responsibility to do so. And finally, you can (You can also set up a hybrid of more than one overhaul trigger. Most small-plane constant-speed propellers must be overhauled every 1,200-2,000 hours or every 12 years, whichever comes first). And finally, you can overhaul on condition, inspecting frequently to determine the condition of firearms and parts. This is how the Army tries to catch their round-limited parts, because they don’t actually track rounds. (They know they should and are trying to work out a way to do it).

For those who are curious, here’s a military guide to inspecting and maintaining the M9 (this is the USMCs. Most Marine ordnance documentation is the same as the Army’s, just renumbered with the Corps numbering system, but this one is USMC specific. Doesn’t mean a soldier can’t learn from it: Inspection-and-Repair-of-the-M9-Pistol.pdf

  • Fifth: Sitting. Sitting untended can be worse for machinery than the wear of daily use. That’s because a sitting machine gives corrosion time to work its evil on the metals. (This is, in fact, why an airplane engine or propeller has a calendar as well as an hourly limit, to catch the “sitters” before corrosion can do them in). Of course, Springfield Armory tests found that weapons could be packed for permanent storage and last for decades without corrosion, but weapons in a ready condition in an arms room are exposed to the atmosphere (but climate-controlling arms rooms is not a sexy budget item).
  • Sixth: Low-bidder parts. The Army and Beretta both have been relentless at driving the cost of the gun and its spares down. As a result, they’e got some schlocky parts in the system. By this we don’t mean the parts that aficionados abjure, but are perfectly serviceable and durable, like polymer triggers; we mean the several versions of self-destructing locking blocks.

Most of these problems also applied to the M1911 when it was at end-of-service-life. The corrosion problems were different on the all-steel Colt versus the steel and aluminum Beretta (where you can also get galvanic corrosion!), but the basic issue of corrosion never goes away: anything that was once part of geology has an inborn entropic urge to revert to ore over time.

And all of these factor in to why the Army wants a new service pistol. They’re not the only, or even the major reason. It seems that the Army is feeling left behind by market trends in service pistols. But they’re likely to solve this entirely the wrong way.

Monday: What’s Wrong With  the Army Modular Pistol Competition (hint: it’s not that it will inspire criminals, like that inadvertent comedian Matt Valentine desperately wrote in The Atlantic).

Barrel Heating: Allsop & Toomey & Rheinmetall, oh my!

Last night, musing over a possible technical post for this morning, we opened Allsop and Toomey’s Small Arms: General Design to see how what they wrote on barrel heating compares with our recent translation of the Rheinmetall HandbookAnd there was the same damned diagram.

No, not a close parallel. Or a close copy. The same jeezly thing. Don’y take our word for it. Here’s Allsop & Toomey:


…and here’s Rheinmetall:


That’s not coincidence; the form as well as the facts of the diagram are identical. Which gives rise to the question: who copied whom? Beats us with a stick. Although the Rheinmetall handbook has some primacy (1973 versus 1999, as the yellowed pages of our copy show) it’s quite possible that both derive from an earlier source. We don’t remember seeing this graphic in Balleisen (our copy of which is still adrift somewhere in office or library) or in Chinn (which we ought to check, because we have the e-book, although we just moved 150 GB of ebooks to our RAID array, which promptly ate a disk and needs repair stat — just reminding ourselves here).

One indicator we see that hints that both derive from some earlier source is that both graphs show an approximation of barrel heating, without numbers. It is the numbers, of course, that are most useful to the designer or engineer, although the graph showing how these numbers are arrived at over time is not without its own utility. The suppression of numbers in both the Handbook and Small Arms: General Design suggests that they’re both using a graph from some earlier technical report. Absence of this graph in US design books makes us speculate that the ur-source may have been European.

rheinmetall_heat_pageHere you can see the two graphs in context on their relative pages. (All images, including these thumbnails, embiggen with a click; the square thumbnails expand to show the full page with legible text, although the Rheinmetall is in German, naturally). What’s more interesting is that the two texts handle the same graph quite differently. Rheinmetall (whose text is translated in our earlier post) explains the graph and its meaning at some length.

allsop-toomey_heat_pageConversely, Allsop & Toomey just throw off a sentence telling you that breaks in firing reduce peak internal temperatures without really delaying the rise of external, overall temperatures. But they also include some numbers, despite the suppression of them in the graph, numbers that are quite useful to you. (All the numbers in both works are in SI units). They suggest there’s a difference of as much as 400º to 100º (C, F equivalents are roughly 750ºF and, of course, 212ºF).

The Britons warn that, if 500º C (932ºF) is maintained, “permanent damage will be done to the barrel through accelerated wear and erosion.” And then they go into a number of useful equations. They do not seem to estimate the point of failure of the barrel with all this sheet music; that is all tied up in pressure as well as temperature and there are an awful lot of variables baked into it; today’s engineers, unlike those of 16 years ago (Allsop & Toomey) or 42 years ago (Rheinmetall) would certainly use something like CATIA to do a finite element analysis of the barrel to substantiate the strength of the barrel in its predicted use, and estimate where and when it would let go.

We do note that the temperatures noted in Allsop & Toomey, and the surprisingly sparse cadence that will produce them, are in line with some of our previous material on the carbine failures at COP Kahler in Wanat (see here and here; the Wanat failures happened in part because soldiers are not taught to understand nor a practical way of avoiding overheating, beyond a simplistic “short bursts” drill) and on heat-driven accuracy problems in the ANM2 .50 caliber machine gun in the USAAF.

If readers would like, we can walk through some of the math. We’ll probably need the Blogbrother’s assistance, as he’s rather better at maths that your humble blogger.

A Note to Readers

This sort of technical post would be banned — would, indeed, be a felony — under Secretary of State John Kerry and his minions’ extreme and un-American attempt to suppress free speech about weapons design. Even though this post is based primarily on two textbooks published in two foreign countries, and available to all the world for decades! The Ivy League inbreds at State base their proposal on the contemptible and flimsy excuse that sharing knowledge constitutes international trafficking in arms.

Meanwhile, those same cretins are negotiating all obstacles out of the pathway to nuclear arms for the most terrorist-sponsoring regime in world history, the Islamic Republic of Iran. Got that? Iran/IRGC/Hezbollah/Hamas, getting nukes? No problem. You, understanding barrel heating, whether you are Iranian, Russian, Chinese, Canuckistani, or, like the majority of our readers, American? Problem. The guy should stick to what he knows, whatever that is. Seducing trust funds off of heiresses, perhaps.


If you would like to keep the First Amendment operative in the United States, and thereby disappoint the man who’s a living parody of Thurston Howell III, here’s a three-point plan for you:

  1. Read the background on the issue from the NRA.
  2. Read the actual notice of proposed rule making (.pdf; relevant bit begins in lower right of the first page) in the Federal Register and make sure you understand it.
  3. Make your comments in your own words about how this regulation works to harm you instead of its ostensible goal.
  4. Comments go here at or by email to: with the subject: “ITAR Amendment—Revisions to Definitions; Data Transmission and Storage”. Ceteris paribus, this link should open in your email application with the correct subject header.
  5. As a backup, contact your Congressman and two Senators. The very best way is to call their direct number; Google is your pal on this. Next best is to call the congressional switchboard (202) 225-3121, and ask for each of them in turn (you do know the names of your Senators and Representative, don’t you? If not, Google again). You’ll either get dumped in voicemail or to a junior staffer or intern, unless you’re a big donor. Have an index card with the points you want to make, make them briefly and politely, and end the call. For example, we have been making the point that a State Department that can take on prior restraint of Internet content is a State Department that is heavily overstaffed and overbudgeted, and might very well give up a few hundred millions in personnel expenditures for the Congressman’s pet projects.

D2S2 here, folks. No threats, no bluster. Make real, substantive comments on how this proposed regulation harms you and yet, does not prevent the sort of arms races and weapons proliferation the State Department usually knocks itself out encouraging.

If you have questions, we will try to answer them.

ITAR is no joking matter. It is an all-encompassing and deliberately vague law — it would even apply, on professor avers, to Superman —  and because it is so large and so difficult to comply with, it’s frequently used as a club to beat political opponents with.

For example, this iteration of the .gov has not been shy about really stretching to try to punish gun-culture figures with flimsy, but very costly to defend, ITAR prosecutions. Our ITAR counsel is telling us the blog has to go (archives and all) if this monstrosity of a rule becomes final.

Do not delay. They are already playing games with the availability of the comments website and email addresses to limit opposing comments.

Expect to hear this from us again.


Allsop, DF and Toomey, MA. Small Arms: General Design. London: Brassey’s, 1999. (Note that this out-of-print text is Volume 6 of a series on ballistics and weapons design called “Land Warfare: into the 21st Century” by authors mostly affiliated with the Royal Military College in Shrivenham, England).

Rheinmetall. Waffentechniches Taschenbuch. Düsseldorf, West Germany, 1973.

A Tale of Two Temperatures

Consider this graphic. It is a somewhat crude reproduction of one in the Rheinmetall weapons design handbook. Secretary of State John F. Kerry, who is unlucky at bicycles bur uncannily lucky with heiresses, thinks that we all should be criminals for discussing this online, so let’s all get our crime on and return to a subject we’ve discussed before, heat management  in automatic firearms.



The original of this graphic is a rather dull monochrome one in the style of the rather dull, unless you are the sort of gun geek that Secretary Kerry dreams of decanting into durance vile, Rheinmetall Handbook. Our copy is the German language version, because we read po-nyemetskiy, and wants $300-400 for an English copy, when there is one to be had, but has copies of this out of print classic for about €100. (Which is going to be lunch money if they keep letting Greece set continental fiscal policy). It took us several iterations to get the slopes about right, and we got the round-count wrong: it’s supposed to be two neat Teutonic bursts of 10, and we have a rather limited and non-Aryan 8 and 9, but with that difference noted, this graphic is  close enough to discuss the phenomena at issue. Here’s what Rheinmetall says about this graphic:

The barrel of an automatic weapon is, as a consequence of the normally high rate of fire, subject to extraordinary temperature demands.

[This illustration] shows the approximate course of temperature of the inner- and outer wall of an MG barrel in two bursts of fire of 10 shots each with a pause lying in between. Feel long, or many short, bursts of fire can drive the temperature of the inner wall so high, that it has a significant influence on the material toughness and therefore on its use and employment.

In this, the cadence of fire, the number of shots in a burst, the pauses, the lengths of the pauses, and the number of bursts of fire fired rapidly one after the other, in conjunction with the thermal resistance of the barrel material and the strength of the barrel walls all play a role.

Comparable barrel-life shot counts can therefore be reached with the same firing rhythm. Often the “French anti-aircraft rhythm” is used: this is 144 shots in 12 bursts of 12 shots each, with a 2-second pause after each burst and a 20 second pause after every four [bursts]. With MG barrels, a firing rhythm of 250 rounds in numerous bursts is often used.

For testing automatic weapons and their ammunition, Rheinmetall has developed an electronic Rate and Rhythm Control Apparatus, which is described below in section 7.7 [of this book].

Measures for increasing the life expectancy of barrels include:

  • Heat-resistant materials;
  • Chroming or Nitriding the interior wall;
  • Progressive twist and rifling profile in conjunction with barrel caliber tightening.

Less effective are cooling fins and water cooling.

Barrels for MGs and machine cannon must be rapidly interchangeable.

Now, this graphic is limited in its utility because in its original version, it comes without any numbers attached (accordingly, we have eliminated from the version we show you, the numbers we used for temperature (ºC; as you might expect the Handbook exclusively uses SI units) and seconds to approximate the original. But we can draw some conclusions based on the shape and gradient of the two lines.

Our take-away is that the key point is that the baseline is higher after each burst, and that the internal temps go higher in each successive round of each successive burst. What does not show on this line is the temperature where the barrel fails. As we have seen in the M4 experiments wherein a carbine was tested to destruction, this happens at a fairly predictable and repeatable, ergo constant from an engineering point of view, temperature. As Rheinmetall points out, several roads will get you to that temperature sooner or later.

Maybe he didn’t know this, but thus is why your sergeant whacked you upside the hemmet and told you to fire shorter bursts.

Looking at the Rheinmetall data, it seems that for their test weapon, whatever it was (MG3?), the barrel recovers its temperature rather speedily after the passage of each bullet momentarily superheats it. We would attribute this to the limited ability of a small projectile’s friction to heat the much greater mass of the barrel — this is also why the internal and external temps diverge so widely. But note that the internal temp continues to ride steadily as long as a steady sequence of pause and fire is applied, and at each pause the internal and external barrel temps have diverged more widely.

The implication is that an automatic weapons barrel is going to be heated to its limits at some point, moreover, at some predictable point, in any continuous fire regime, and while some of the magic designers have used over the last century, like chrome plating and stellite liners, can give you some more rate of fire on the margins, only changing out the barrel (not usually possible in a light automatic carbine) or otherwise giving the barrel a chance to rest and recover from high temps will prevent failure.

Thus endeth the lesson. Apart from further education which may come in the comments.


Geissele (ALG Defense) AK Trigger

Bill Geissele’s wife’s company, ALG Defense, makes products for more of a mass-market than the very sweet, fairly simple, Geissele AR-15 triggers that live in more than a few SOF M4s and Mk. 11/12/18s, etc. (Indeed, sometimes the Geisele triggers are authorized MFP 11 or unit purchases, and sometimes they are installed on a catch-me-F-me basis by unit weapons men or armorers). Along with the triggers for full-on M4s and HK416s, Geissele makes improved triggers in both single-stage and two-stage variants for a wide range of semi ARs. They’re not cheap, they’re not always in stock, but they’re good.

ALG Defense makes simpler AR triggers — and now, an AK trigger, imaginatively coded AKT. In this video Bill explains the objectives this trigger meets and talks about some of the challenges involved in designing it.

The AK, Bill says, “has a ton of sear engagement.” That’s what you, the shooter, perceive as the very long and very smooth takeup of the typical AK trigger.  (The SKS trigger has a similarly long, smooth engagement, suggesting that this may have been a standing Soviet / Russian design objective).

The result is an AK trigger that fits a variety of common receivers on domestic, imported, and kit-built AKs, and that reduces the trigger pull force and duration (including that all important very long sear dwell) significantly.

For example, Bill shows a graph of a stock AK trigger versus the ALG AKT; the stock trigger moves about 0.150″/4mm and takes about 4.5-5 lb. of pressure during that sear dwell period. The AKT takes up the slack more quickly and seems to come in about 0.065″ and just under 3.5 lb.

At about 8:30 he shows a 3D model (in Autodesk Inventor) of the trigger and walks through its function.

It fits some AKs with no fitting, but because of the wide variation in AK safeties, some AKs need a roll pin positioned so as to contact the safety. It’s explained in the video and in the AKT’s instructions.