Category Archives: Weapons Technology

Gun Maintenance by Sound Principles

Remember what we’ve said about maintenance before: a gun is a machine, and maintenance is like maintenance of any other machine. Every firearm contains several classes of parts. Some of these parts may be so over-engineered they’ll never fail; other, parts that the manufacturer expects that you will replace (like the battery in your car, or springs in your gun, or wipes in an old-style suppressor); and still other parts can be expected to wear out depending on how hard you use them — parts that will fail due to wear or fatigue if not replaced pre-emptively.

Failure from overstress is another thing entirely. You can blow up any gun with Uncle Bubba’s Dynamite Hot Loads, even a perfectly produced firearm straight out of the box for the first time with the dealer’s hang tag still dangling from the trigger guard.

The parts you need to prepare to replace are the ones subject to physical wear and to fatigue failure. And there are several ways to do it. You can replace parts that are subject to wear and fatigue failure:

  1. When they actually fail. A lot of people do this, and if it’s not a machine that you depend on for life, Replace On Failure works just fine.
  2. When an inspection reveals that the parts are showing signs of imminent failure. At the risk of overstating the obvious, this means you have to conduct inspections on some sort of a schedule timely enough to find bad parts before they fail… or your Replace On Condition plan becomes unplanned Replace On Failure.
  3. When a certain interval has passed, which might be a calendar schedule or might be number of operating hours or cycles. This approach is called Replace On Schedule; and whether it’s a good or a bad plan depends on the devilish details of the case.

Modern firearms are much more reliable than their historical forbears. And modern ammunition is, as well, plus it also tends to be noncorrosive.

Another part of maintenance is cleaning. How frequently should you clean your guns? The answer may surprise you. Given modern designs and materials, noncorrosive ammunition, and reliable modern systems,  the real requirement to clean an AR or a Glock is this: when it absolutely needs to be cleaned because the mung buildup has begun to interfere with the firearms’ functions.

Here’s a picture of Kyle Defoor’s glock, as it came up for on-condition maintenance and was immediately scheduled for a cleaning.

DeFoor Funky Glock


The pistol was essentially never cleaned. You’re looking at 7,500 rounds of baked-on range mung, and it was still working, but the slide had started slowing down.

Many people overclean their weapons, wearing the protective finish off and exposing their guns to the risk of corrosion. How come, when Kyle’s pistol shows it’s not necessary (and many others, Mountain Guerrilla comes to mind, have gone even longer between cleanings on rifle platforms). If it’s designed right, manufactured right and assembled right, it’ll keep rocking, or, as in this case, Glocking.

So why do we overclean? History, and culture. Used to be priming compounds like fulminate of mercury or lead picrate, and some chemicals in propulsive powders, were deadly to firearms. Thorough, frequent cleaning was the last line of defense. Now it’s come full circle — cleaning can actually put fine old firearms at more risk than leaving them alone!

3D Printing Roundup, Number Whatever (Video / Image rich)

Did you know 2016 is the Year of Building Your Own Gun? It is. Get to it!

OK, here’s a new video on printing and assembling the Bolt lower, a bolt-together AR lower.

We’ve featured the Bolt many times before (including links to its files) but this is a new video. The names involved (Ma Deuce, RollaTroll, FOSSCAD, FP [Freedom Print]) should be familiar to everyone.

The Bolt looks like it easily would be modified for assembly with rivets, if you don’t like the idea of parts unscrewing themselves. Several mods of the Bolt already exist, like one by Warfairy adopting the profile of the Vanguard lower, and dispensing with any provision for a safety.

Homemade Charger How To

If 22 is your thing, here’s an Instructable (!) on doing a pistol based on the Ruger Charger design.

3DP Ruger Charger

The creator is another old familiar name, Buck Ofama. Sounds vaguely foreign; do you think that’s his real name?

Reminder, Here’s the Latest File Repository, “Ishikawa”.

Can’t go the mile if you ain’t got that file.

Some New Stuff — no Files yet

Ambi mag release for the Glock-mag Gluty pistol, based on Glock and AR parts.

Gluty ambi mag release

Treillage (sp?) competition stock from Warfairy — gives lots of adjustments on a regular carbine receiver extension. How it looks on the gun:

printed stock on firearm

How the parts break down, color coded:

treillage stock

Bear in mind that anything that’s still just a rendering, puts you on the bleeding edge of the tech when you go to print and use it. But for some of us, that’s half the fun!

New Videos from Guy in a Garage

We’ve already seen GiaG print, remove support material, and assemble a Vanguard AR lower in ABS plastic. But he’s been on a roll lately.

Here, he takes the Vanguard to the range — 300 Blackout with his homemade suppressor. (He blanks out his suppressor markings for privacy. Not that “they” don’t know, as it’s a registered receiver). After firing 60 rounds at the range, he analyzes the condition and performance of his lower.

Want to make your own suppressor like he did? Here he covers the regulatory issues.

He has printed at least three different AR lowers. Here he preps and assembles a Phobos, in ABS:

Here he preps and assembles a Charon, again in ABS:

Important note, he previously printed an early model and it was “off” dimensionally — this one is the 4.0 version.

And here’s a range safety bolt/chamber block for the AR. If printed in nylon, these would be oxen strong and easily dyed orange…. unfortunately we don’t know if he has released the files.

Some of these accessories are cooler than entire 3D Printed guns.

Case Trimmer Insert

Reloaders swear by the $70 Little Crow Gunworks’ WFT — World’s Finest Trimmer. The WFT2 version lets you use the same trimmer for multiple calibers with a $30 interchangeable insert (instead of a whole second trimmer). So Guy in a Garage printed his own insert for the WFT2 for .300 Blackout. This video shows it and tests it out.

Is this the first Registered 3d Printed Firearm?

Michigan has some weird laws. (Every state has a few). So the guy who made this Washbear is arguably the first manufacturer of a registered 3D Printed firearm, unless some poor wretch in the People’s Republic of Massachusetts, the Cosanostrian Emirate of Cuomostan, the Alternative State of California, or some other dystopia has done so already.

Registered Washbear

The cylinder has lined chambers, and is printed of Taulman 618. If you look closely, the pistol unlike the standard Washbear, has a frame made in two parts and joined by screws (and glue). That’s because this builder’s printer wasn’t big enough to print the whole Washbear frame in one shot.

The whole Imgur thread is worth reading in depth, as almost every picture has an informative caption. Enjoy!

How about some Tech on Carbon Fiber filament

Is “carbon fiber” and other exotic filament for normal FFF printers really that much stronger? Joe Binka, Lead Design Engineer for large-format-printer maker 3D Platform, wanted to know, so he did a very engineer thing and, making a test coupon and testing the coupons to failure, evaluated all the extra-strength filaments he could get his mitts on. (3D Platform’s printers use the same FFF technology as all open-source FFF printers, and can use all the same materials). The results were a little surprising.

3DP materials test-result

In this color map, redder is better and greener is worser. Joe discovered that while polycarbonate was the strongest, it was such a pain in the neck that he recommended the runner-up, PC ABS, instead. Polycarbonate…

is a pain to print with. It warps and curls really bad and I would rather avoid it if possible.

…. If I need a really strong material, I’m going to go with the PC-ABS over the carbon materials. It’s just much easier to deal with.

Joe has promised to add new materials to the chart, as they crop up.

Before There Were Many 9MM Ultra Compacts, There Was One

Devel ASP 12Before there was the current rich supply of ultra compact 9 mm pistols, someone had to have the idea for the first time. In fact, the idea of a small 9 mm carry gun was widespread long before any factory produced one.

The market answered, after a fashion: cut-down versions of pistols were produced. Some of them weren’t cut down much, like the P-38K and the Colt Commander. Others were not really practical, like Baby Lugers, and always appealed more to collectors than self-defense carriers.

SW-semi-model-chartBut the natural host for these first-generation pocket nines in the 1970s and 1980s was America’s first pistol designed for what was then a European cartridge, the 9 mm Smith & Wesson Model 39. The M39 was a postwar design that sought to blend European and American design concepts, and not only did that but produced an attractive firearm at the same time. It combined a Browning-style tilting-barrel, and a Walther-like SA/DA operating system with a slide-mounted safety/decocker. Mag release and slide stop were also Browning style, and the barrel was positioned in the nose end of the slide by a collet bushing modeled on the one in the Colt Gold Cup.

The M39 was single-stack before single-stack was cool, and entered the market in 1954-55 after years of development. If you want to foray into the weeds of Smith auto pistol history, Chris Baker took a shot at decoding Smith’s nomenclature mess with the M39 and its legions of successors at Lucky Gunner Lounge last year, also producing the infographic on the right, which appears correct but incomplete.

But the reason that the M39 yielded those early conversions were (1) it was readily available, and (2) there was nothing vital and hard to relocate in the parts of the gun that a compact conversion hacked off. This picture from an S&W forum shows three cut-down 39s: from l-r, an Austin Behlert special on a Smith 59 (basically, a double-stack 39), a full Devel on a 39 with ambi safety, and a full devel (no ambi safety) on a 59.

Behlert Devel Devel

The first, and most exotic small Smith was the ASP, made beginning in 1970 by New York artist and espionage agency hang-around Paris Theodore, who partnered initially with George L. Nonte. This ASP picture comes from the same forum as the shot above, and illustrates the somewhat industrial finish on ASPs.


The magazine was patented, specifically for the unusual laid-back pinky rest. The open side made the transparent/translucent segment of the grips practical.

One of the ASP features that will never show in a side view is that about 40% of the width of the reshaped trigger guard was milled away on the strong side of the customer, to provide faster access to the trigger. Theodore claimed that an ASP had 212 modifications from the factory M39.

Theodore’s spy stories seem to have been cut from whole cloth, but he died young — here is an interesting, if credulous, obituary in the late, lamented New York Sun. A definitive ASP was trimmed in height and length, dehorned and softened in its angles, and fitted with a patented “Guttersnipe” trough sight and see-through grips to facilitate round counting.

The Devel was devel-oped (you may groan) by Charlie Kelsey. They tended to be better finished and often had fluted slides to reduce weight. Here are three Devels, a 59 and two 39s.

Three Devels

This is a Devel on a Smith 39-2 from a current GunBroker auction, but supplied with two ASP magazines.

Devel ASP 09

The seller says this about it:

Smith & Wesson Model 39-2 Devel Custom chambered in 9mm with a 3.5″ barrel. Used but in good shape! Frame and slide have some handling wear, couple scratches, and little bit of finish wear around the edges. Comes with two hard to find ASP magazines! Please look at the pictures for details.

Devel ASP 05

The cut-down for Devel and ASP alike was usually 3/4 of an inch to the barrel and slide, and about a half inch to the butt. The package usually included replacing the collet bushing with a plain bushing, on reliability grounds, and bobbing the hammer.

Devel ASP 06

As you can see, the gun is not only shortened but also “softened” or “dehorned,” but it’s not what Devel called a “full house” custom, as it lacks the squared-off trigger guard and lightening flutes in the slide.

Factory compacts like Smith’s own 3913 crippled the market for these niche firearms, and both ASP and Devel folded, victims of the success of their own product.

Like Paris Theodore, Charlie Kelsey died prematurely, but while Theodore lost a long and debilitating battle with disease, Kelsey was found shot and burned in a ditch in Georgetown, Texas. While there were indications he may have been suicidal, he certainly can not have set his own dead body on fire. His murder has never been solved.


Of course, true Dedicated Followers of Browning would not be caught dead with a 9mm flyswatter: their pistol-shrinker of choice was Detonics, or Behlert (who called his bobbed .45 the Bobcat). But that’s another story!


3D Update for 8 April 2016

Here’s a few things that may be useful or entertaining to people working with, exploring, or just interested in this technology.

AR-15 Printed Lower: Print Bed to Ready to Load in 20 min

This video shows what appears to be the real time assembly of a FOSSCAD Vanguard lower from the print bed to a complete (if sightless) AR.

We’d quibble about some of his shortcuts and techniques — no, a piece of copper wire is not a suitable substitute for a roll pin, and while it’s neat that he used 3D printed pivot and takedown pins, how are they retained? Oh, they’re not — but we’ve been telling you for years that this technology was maturing, and now we’re showing you.

We suspect this fellow’s channel is going to be worth watching in the future.

Shuty MP-1 by Derwood Night Fire (10 sec. video).

We’ve discussed the gun before, here’s a video of it shooting at night.

Unlike his earlier versions of the Shuty, Derwood won’t be publishing these files on SendSpace. He also notes that the MP-1 still is limited; 18 rounds is all it takes to soften the thermoplastic around the barrel. Of course, he’s already working on improvements, as an intellectual exercise in home workshop engineering.

The media reaction to his firearm has been… interesting. Even 3D Printing industry journalists are journalists at heart, and can’t see this except through the prism of their anti-gun politics. For example, Benedict at tut-tuts that “the relatively new phenomenon of open-source, downloadable firearms seems to promise a greater deal of harm than good,” whines that, “the maker circumvented all gun control laws, creating a totally legal weapon without so much as an ID check,” and closes with, “So is it sensible to put lethal weapons in the hands of all and sundry with an internet connection and 3D printer?” Andy Greenberg at Wired, long prone to involuntary incontinence in his Aeron over this issue, hyperventilates similarly: “Deadly, working guns that anyone can generate with a download,” that have “spooked gun control advocates” — those unnamed “gun control advocates” being named, naturally, “Andy Greenberg” — and “successfully circumvented all gun control laws”.  Our only question to Benedict and Greenberg is, “With your string of pearls in one hand and your blankie in the other, how do you type your articles?”

3D Printed Rimfire Stuff

We had been unaware of the 3D action over on, a membership forum. Lots of 3DP based threads there, including:


Spud Gun Camera Module

GoPro Spudgun roundNow we get silly. Here’s a “projectile” that lets you fire a GoPro camera from a spud gun and recover the camera, rather than see it dashed to pieces. Well-engineered, with spring-loaded stabilizing fins just like “real” FS smoothbore rounds. You’re on your own for more martial applications, and mind the Destructive Device laws.

Yes, this is very silly. And?

Mark One Reinforced Printing

This is the Mark One in action. This is not ours, it’s Sumdood’s, but we finally have time to work on ours this week! The Mark Two is even cooler as it can winkle the reinforcing fiber into smaller areas… the Mark One can’t turn the reinforcing around a corner any smaller than the size of a quarter.


Exotic Fibers for Everyday Printers

Of course, the Mark Forged printers require proprietary fibers. But exotic fibers are becoming available to open-source printer users as well. Here’s an enthusiastic young Australian named Angus showing off a quadcopter frame with arms of four different materials: common ABS and PLA, and exotic Thermoplastic Polyurethane (rubbery) and Colorfabb Carbon Fiber (rigid).

One of Angus’s really good ideas: using a raft of ABS as the basis for the exotic print. (A “raft” is an expendable base laid down underneath the “money” print). The sales page for the TPU says don’t use rafts, and that’s because they mean, rafts of TPU. He also didn’t heed the warning about using steel nozzles with the carbon fiber, and he explains why.

Instead of laying continuous fiber reinforcement like the Mark Forged printers, the Colorfabb XT-CF20 “Carbon Fiber” filament seems to have sort of chopper gun microfilaments in it. The trade off is less reinforcement strength vs. more flexibility of employment.

Of course, the Mark Forged printers also use nylon as their basic material. Nylon. as we have seen, has significant advantages over PLA or ABS. (One of the nicest things about it is it does not emit a noxious smell).

Check out his channel, Maker’s Muse, it’s full of interesting stuff. He also has a video on “metal” filaments that you may have seen advertised.

Taulman3D Materials

Speaking of materials, especially nylon variations, but also a “better” PLA and an elastomer, all kinds of new stuff from taulman3D. Lots of horses for lots of courses there, and that link’s just their new stuff.


Know those Shuty 4.0 MP-1 files that derwood wasn’t going to release? Well, he didn’t, but….


What Does this Rock have in Common with These Guns?

It’s poll time! What does this funny looking rock have in common with these guns?

Cabot Rock Guns

What do the rock and the gun parts have in common? free polls

Answer? You know it: after the jump!

Continue reading

A New Rifle, a Reliability Problem

question mark(Apologies to all for the premature launch of this post at 0600 this morning. It was originally supposed to go there, then it was moved to the 1100 spot but the night shift botched the job. Those responsible have been sacked. Your comments and poll elections should be preserved.-Ed.)

The rifle had been praised wildly on the occasion of its adoption. Years of testing had proven its superiority, and it offered a revolution in rifleman’s firepower. Some of the claims made for the new rifle were:

  • Greater accuracy in combat conditions;
  • a greater volume of fire, firepower equal to five of the old rifles;
  • more effective against modern threats;
  • less demanding of training time;
  • lower recoil, and negligible fatigue from firing;
  • average size of production rifle groups, 1.75″ extreme spread at 100.
  • accuracy “better than the average service rifle, compares favorably with [a customized target] rifle”; and,
  • “every organization so far equipped has submitted enthusiastic reports of their performance under all conditions…”

Despite that glowing report from the men responsible for the decision, reports began to trickle in of unusual, crippling, and intermittent stoppages, and this reinforced many servicemen in their reluctance to give up their Ol’ Betsy for this new piece of technology.

What Rifle are we Talking About Here? free polls

Answer after the jump!

Continue reading

Some 3D Printed Firearms Updates

It’s been a long time since we did one of these updates, so here are a few things we’ve picked up here and there.

Print Now, Rest Later

Here’s a practical print task: a 3D printable cheek rest for an AR-15 pistol. (Well, to the extent that an AR pistol is practical). As we understand it, if you shoulder the weapon (say, with a SIG brace) you are violating the SBR laws, but if you’re cheek-resting you’re all tickety-boo. This image is a rendering; a final print will have some striations to it, from most printers using the most common 3DP technologies.

3D Printable AR pistol cheek rest

Checked as of last night, the files are here:

Happy printing & shooting.

About those striated parts

One of the problems with 3D printing, especially the Fused Filament Fabrication / Fused Deposition Molding type that is common, is that the parts often display layering, striations, and other artifacts that add up to a lousy surface finish. There are several ways to smooth 3D prints.

These include:

  • Mechanical Smoothing — this can be sanding or particle blasting; each has its pros and cons. Sanding is limited in how small a part you can do, bead blasting in how large. Bead blasting always produces a matte finish, although the coarseness or fineness of the finish depends on the blasting media. On a part large enough to be practically sanded, sanding can produce a finish limited primarily by time and the cost of skilled labor.
  • Chemical Solvent Smoothing — this involves exposing the part to solvent vapor. For example, for ABS, acetone vapor either cold or hot (hot vapor has definite safety limitations and concerns, but can produce a superior finish). Acetone doesn’t work with PLA as it’s not acetone-soluble. Acetone also reduces the strength of the part: its stiffness is reduced, and it fails under a lower load.
  • Finish Coating — for a cosmetic finish, a thick paint can be used to fill layer striations. This will, often enough, loop you back to sanding. This is cosmetic only and subject to wear.
  • Epoxy Coating — this does require some skill to pull off, but both fills and reinforces the part. This can be important with some liquid-based and powder-based laser 3D printers whose parts tend to be brittle; coating them with epoxy can make the printed part, in effect, a shear web and form inside a tough, flexible epoxy shell. This is good when the part needs to be employed as is, and not so good if the part is intended to be, say, a sacrificial casting pattern. (In that case, for lost-PLA casting for example, use one of the other procedures). Smooth-on sells an epoxy that’s optimized for this type of use and has several how-to and application videos on the web page.

For more information:

  1. Lindsey Frick in Machine Design on “How to Smooth 3D-Printed Parts.”
  2. Smooth-on’s gaudy page on their XTC-3D 3D Print Coating has lots of examples and tutorials.
  3. Here’s Make Magazine and Instructables with a pair of acetone-vapor tutorials.
  4. And here’s the story of a guy who went whole hog and built an ultrasonic vapor fogging chamber in hopes it would increase the strength of his prints (it actually weakened them). There’s a link in that article to an Instructable on building his fogger, too.

100 Rounds from a 3DP Pistol

Remember the original Liberator (well, the original 3D Printed Liberator, not the original original Liberator)? It was only good for a few shots. (Unless you were the New South Wales Police, and printed it without reading the instructions, in which case it blew up first shot). What use was it? But as Franklin said on being asked that of the invention of the French aeronauts, the Montgolfier brothers, “What use is a newborn baby?”

Well, here’s a 3D Printed pistol that has fired 100 rounds and is still going. 3D printed AR lowers long ago beat that number, but here’s a pistol that’s all 3D printed on consumer equipment, except for the mandatory weight and firing pin.

100-round-songbirdWe’re not sure whether this colorful print of this James R. Patrick design wants to be a toy, or whether it wants to be a Glock when it grows up.

A Practical Print for Almost Everyone

What’s this? It’s an AR Hammer Block. Use it when you want to function-check that lower you just monkeyed with, without running aground on the Scylla of letting the hammer slam into your expensive piece of aluminum (very expensive if it comes with a stamp), and the Charybdis of using your delicate pink (brown, whatever) thumb to intercept the falling hammer.

printed AR hammer block

A great, practical print. (The website it’s advertising is for a training device to use with your SIRT, not available to the general public yet). Hmmm… the “files” link at, went to a malware site:! And downloaded a malware .exe! We’re not giving you that link.

OK, here’s another one instead, by Charles Lacey:

AR trigger pull test block

Files here, Grabcad is not a malware site: (You do have to join Grabcad to download files, though).

Lacey also has a chamber flag, or as he calls it, a bore flag, on Grabcad, and a couple of Magpul mag floor plates, including a whimsical Flying Tigers version. We leave finding those as an exercise for the reader.

Large Format Printed Pistol Now Speaks Glock

shuty mp-1 pistolWe’ve showed the Shuty MP-1 before, a 3D printed pistol inspired by the designs of Luty. The pistol made a splash in the media some time ago, with the usual alarums and excursions, dogs and cats lying down together, and all the usual drivel you usually only hear in an election year. (This happened twice, actually — in February 2015 with the original Shuty, and in February 2016 with the improved MP-1).

Less publicized has been the Gluty — as you can see from the image below, it’s a Shuty reengineered for Glock mags. The image tells us it’s been printed but we’re not aware of how successfully it has been test fired — unlike the Shuty.

Gluty 3DP pistol

One of the biggest limitations of the Shuty is its magazine. Adapting to commodity Glock magazines is the easiest way to increase the magazine capacity of  this novel firearm. At the same time, the original files, with their included magazine files, allow the creation of a firearm where even the mags are unobtainable.

Of course, that still leaves the barrel as a tough nut to crack. Shuty and Gluty use the standard pistol barrels.

Printed AR Lower

This FOSSCAD JT Vanguard has been around for a while. This recent print, in ABS thermoplastic, shows some of the strengths of the design, and how the venerable AR form factor has had to change to adapt to these new materials and new processes. First shot shows it with an upper in the white. The grip and magazine are also printed.


The grip is also ABS. We’re not sure about the materials of the mag, and wonder if the buttstock is printed also. This next picture shows you just a few of the changes, including the bulkier pivot area, the much beefier buffer tower, and the thick reinforcements along the receiver outboard of the trigger group.

FOSSCAD Vanguard JT ABS CloseThis picture shows the trigger group in place. The reinforcement is clearly visible.

FOSSCAD Vanguard JT internal

There have been experiments with printed trigger-group components, but so far, they haven’t been very impressive. Materials and processes need further improvements.

Exotic Lower-stock Bipod Combination

This is the Atlas AR-15 lower, by WarFairy CAD. It has a certain FN P90 vibe to it. It’s meant to be used with a free-floating barrel and suitable handguard/rails system.

WarFairy Atlas

When one looks at some of these designs, one is reminded of Donald Sutherland’s character in The Dirty Dozen, impersonating a general. “Pretty, but can it fight?”

Atlas Files:

Finally — MakerBot Hates You

MakerBot continues its extreme antigun position. How extreme? A design for a powder knob for a Dillon progressive reloader was banished to 404.

Funny, their 404 page says, “There is nothing awesome here… yet.” Well, there was before they deleted it!

MakerBot does not want our business? Transmission received.

Consider Ultimaker. Ultimaker advertises on, which is an interesting site to check from time to time. Beware of any of their links to Two we observed were both delivering malware yesterday, and probably still are.

Specific Power Trends in Firearms and Engines

Let’s play Igneers! And we’re going to talk about specific power and improvement.

As engineering gets better, a machine capable of delivering power X at weight Y is either replaced by one capable of delivering power X at weight A, where A < Y, or one capable of delivering power Z at weight Y, where Z > X. In some cases, both the power and weight improve, which is to say, they go up and down respectively, at the same time.

Mk108 30mm with its drum. Specific Power champ of the German Luftwaffe. Rendering: Paul Tosca

Rheinmetall-Borsig Mk108 30mm with its feed drum. Specific Power champ of the German Luftwaffe. Rendering: Paul Tosca

This is true for all types of machinery from steam locomotives to Formula 1 motors to (more to our point) firearms. One of the insights in the Rheinmetall  Handbook on Weaponry is that the same concept of Specific Power as used in automobile engines can be applied to firearms, although their example uses aircraft guns (a Rheinmetall specialty for 80 years) as its source data. It is found under heading 7.5, Performance Considerations, on p. 288, and says this about using a specific power comparison:

For an evaluation of the physical power achieved with machine guns, the comparison with heat engines is available. As with a piston engine, chemical energy is released in a periodic sequence in automatic weapons. In an engine, the mechanical part of this energy appears as drive energy through the crankshaft; a smaller portion of this mechanical energy is used for the control and charging function (intake). The mechanical energy, which is gener­ated during the operation of an automatic weapon, appears as kinetic energy of the projectile (and the flowing propellant gases); here also, a smaller portion is used for control and charging function (transport and feed of the cartridge).

In the case of this Mk108, like any automatic weapon, most of the energy propelled the projectile out of the barrel. Some was wasted as heat, and some was used to lift this belt in any G situation and load the next round. Tosca rendering, again.

In the case of this Mk108, like any automatic weapon, most of the energy propels the projectile out of the barrel. Some is wasted as heat, and some is used to lift this belt in any combat attitude and acceleration (G force), and load the next round. Tosca rendering, again.

In order to make the thermal and mechanical loading on auto­matic weapons clear, the criterion of weight per kilowatt can be employed. The specific power weights, which are computed from the kinetic energy of the projectile, the rate of fire and the weight of the weapon, are summarized in Table 701 for different 20 and 30 mm caliber automatic cannons. In addition, the particular year of development is given. At the end of the table, the specific power weights for automobile engines, as well as racing and aircraft engines are noted.

So specific power, whether of a heat engine or a firearm, is a simple power to weight ratio, expressed in SI units for convenience (kg/kW). An adaptation of Rheinmetall’s table 701 follows.

Table 701. Specific Power Weights of Automatic Cannons and Internal Combustion Engines.
“Heat Engine” Caliber (mm) Year developed Specific power weight kg/kW
2 cm 30 AA cannon 20 1930 0.29
2cm 38 AA cannon 20 1938 0.15
MK 202 automatic cannon 20 1967 0.07
Vulcan cannon 20 1956 0.03
MK 108 automatic cannon 30 1941 0.14
HS 831 automatic cannon 30 1950 0.05
D.E.F.A. drum cannon 30 1954 0.04
Automobile engines (over 1.3 liters) 6.1-3.5 (4.5-2.6 kg/HP)
Racing car and aircraft engines 1.1-0.4 (0.8- 0.3 kg/HP)

As the article in the Handbook points out, these automatic weapons are much more efficient than auto engines (having about 1% of the specific weight) and even than the more-optimized racing and aerial engines (about 10% of the specific weight).

What the table makes clear, and the article doesn’t mention, is the improvement over time in specific power weight. Prewar and wartime guns required some number of tenths of a kilogram per kilowatt of output; by 10 years after the war, only hundredths of a KG were required (mostly due to rate of fire increases), and the least of the postwar weapons mentioned is still twice the weight efficiency of the most efficient German wartime gun, the 30mm Mk108 used in the nose of some Me262s and the wing roots of the Me163B.

It would be an interesting exercise to develop such a table for infantry arms as well.

We believe that these improvements have two characteristics, in terms of trends. First, they show stepwise activity, large leaps forward when a technical breakthrough is made (and quickly copied). Second, the long term improvement is asymptotic in nature, meaning early, great improvements have been supplanted by much smaller incremental improvements and as time has passed, the improvements haven’t stopped, but have gotten smaller. But those are hunches; a much larger data set will be needed to confirm or contradict them.


Why They Inscribe the Caliber Right On the Gun

Because sometimes the wrong caliber will chamber. Results, FOOM.

M4 blowd up 01

A guy posted these pictures on ARFcom, saying he wasn’t the shooter/owner, but basically, “it just blow’d up” and he has no idea what happened to it.

M4 blowd up 02

Well, that’s why you pay us the big bucks. This is not a mild AR kB! that traces back to an out of battery fire or one lousy handload. In this case, 100% of the round’s energy came back through the firing pin hole in the bolt face. And shattered the bolt and carrier. What could make an AR do that?

An obstructed barrel right at the chamber. Period. Sure, there’s a vanishingly small possibility that you got a rare combination of a round loaded with pistol powder with the previous round being a powderless squib, combined with a tight bore and wide bullet so that it didn’t go the usual 7-8″ into the barrrel. But the 95% probabilty is: .300 Blackout round in a 5.56 rifle.

He doesn’t know what happened, our fourth point of contact. He claims it was ordinary M193 5.56. Hmmm. Maybe the other rounds in the mag were, but we’re betting there’s a .300 supersonic slug lodged in there.

Go back and compare the pictures of 7.92 x 57mm ammo fired in .30-06 (7.62 x 63) chambers from TM9-2210. Like this incident, they destroyed the bolt, whereas a squib barrel obstruction normally destroyed only the barrel. Conclusion: same kB in a new century, this. (Worsened by the higher chamber pressure and sharper pressure curve of 5.56/.300 relative to the WWI vintage loads, and the bigger caliber mismatch, 2mm+ versus 0.03mm).

(Aside: if you could do that without detonating the gun, which you can’t, you’d get some laserlike velocities on the Gerlach squeeze-bore principle. And you’d get the miserable barrel life that squeeze-bore rifles have always featured).

One of the guys in the ARFcom thread made an insightful comment, that the excellence of the Stoner design is why this guy is not in the hospital (or the pathology lab awaiting dissection). And Stoner did design the AR, all the way back to the 1955 or so AR-10, to fail safe. But this discipline of firearms safety engineering wasn’t born from the brow of Eugene Stoner alone; for decades prior, engineers had been concerned about managing energy pathways in case of structural failure of their weapons. It’s been good design practice for well over a century.

You have probably heard about the “not safe to fire” early Rock Island M1903 rifles. The bad heat treating some early rifles got was only discovered when the rifles detonated, but most of the shooters were unhurt or quickly recovered. That was because the designers of the M1903 in Springfield, and the designers of the 1898 Mauser that they copied, considered and developed safe exit paths for energy in the case of a kB! from an obstructed barrel or other overstress.

If you look at many early centerfire rifle designs you will see that the designers incorporated such concerns to a greater or lesser extent. It’s just design best practice, and it’s universal now, or it should be. Hell, it was universal 120 years ago, which is why it’s nice to have guns designed by engineers and not by Cousin Bubba the Gunsmite.

While “safety” in design can only save the shooter from a beheading (or blinding) by sacrificing the gun itself, we ought to think about We should consider some operational methods to prevent loading .300 BLK into a smaller-caliber rifle chamber, but perhaps that’s another post. The root of the problem (whether it’s 7.92 in a 7.62 chamber, or .300 (7.62) in a 5.56), is that the larger-caliber round fits in the smaller-caliber chamber. (Even a .300 BLK subsonic round can me made to fit with enthusiastic application of the forward assist). You can’t design around a problem like that poka-yoke1 style, you need an operational fix.


  1. Poka-Yoke (PO-ka-YO-kay, roughly) is a Japanese term for design that imposes safe- or correct-practice constraints on the user; Japan being Japan, it’s a kinder and gentler version of their term for “idiot-proofing,” which they watered down verbally — the term, not the concept — for cultural reasons. There are different poka-yoke approaches and one might be better than the next. For instance, the power adapter cord that would only go into an early iPhone one way (the right way) was a poka-yoke, as is the improved one in later iPhones that works safely in either orientation (any way is the right way). Silicon Valley was very quick to adopt poka-yoke as a concept. It has great uses in industrial control and inspection; check out this section of one of Shigeo Shingo’s books (Google Books link).

Burst Selector: An Idea Whose Time has Come and Gone

Burst selector. In this case, on an FNC.

Burst selector. In this case, a 4-position (S/1/3/A) on an FNC.

A couple of years ago, the Army gave the lousy three-round-burst selector switch that was used on the M16A2 and successors, and the original M4, two in the chest and one in the head. There are still firearms with the bad trigger mechanism kicking around the services, but this decision was the beginning of the end of a gadget that was beloved of ordnance officers and log dogs, but utterly loathed by the guys who actually had occasion to launch those bursts in the direction of an armed enemy.

Burst mode has been experimented with almost as long as automatic firearms have existed; for example, some sources claim the 1890-1900 Italian Cei-Rigotti carbine was so fitted, although the best Cei-Rigotti source on the net, this page at Forgotten Weapons, doesn’t mention it.

Ultimately, this bit of 1960s technology was adopted in the 80s by the US Army and USMC, and had about a 30-year run in service, but it’s on the way out, with many powers opting to arm their men with a conventionally select-fire assault rifle, with safe, semi, and full-auto settings.

This is primarily because a burst selector solves a problem that doesn’t really exist with trained troops: troops firing rifles and carbines as if they were great-grandad’s water-cooled Maxims. Anyone can be trained and led to fire short, effective bursts, and anyone who’s been well trained uses an assault rifle in semi mode well over 90% of the time.

The New Zealand MARS-L is typical of current assault rifles: conventionally configured, AR based, and lacking a burst switch.

The New Zealand MARS-L is typical of current assault rifles: conventionally configured, AR based, highly modular, and lacking a burst option.

Where the burst-selector option is ordered, as it was by the mid-1980s USMC and Army, it’s often because logisticians and ordnance guys are having fantasies about all the money they can save in training, and a reduced logistics burden in combat, by taking the Talk To A Crowd® setting off their Joes’ automatic rifles.

They always seem to reach this blinding beacon of brilliance without much interface with combat guys, who are comforted by the security blanket of a Crowd Control switch, even if they’ve never needed or used it. Because when you do need it, you need it urgently.

There have been a wide range of burst selectors proposed over the years. Colt seems to have cataloged, at one time or another, at least one of each!

The most common burst selectors, though, have three or four positions.

  1. The three-position selector is usually configured Safe/Semi/Burst, with the burst usually being 3 rounds, sometimes 2 or 4. We use this form of shorthand: S/1/3.
  2. A second variation, seldom seen, is Safe/Burst/Auto. S/3/∞.
  3. The four-position selector is usually configured Safe/Semi/Burst/Auto. S/1/3/∞.
  4. It’s not, by definition, a “burst” selector, but the widespread safe/semi/auto selector we render as S/1/∞.

It’s also possible that a design separates the safety and fire-control selector. Weapons that did that included the M1918 BAR, the M2 Carbine, and various German select-fire weapons, like the MP.44 and FG.42. It was only postwar, with the HK/CETME system, the AK, and the AR-10 and successors that the idea of a combined safety/selector became the global standard.

Recent purchases have tended not to include a burst selector.

Recent (2015-16) Infantry Rifle Purchases and Competitions1 (not comprehensive)

Nation Model Caliber Fire Control Replaced/-ing?
US M4A1 5.56 S/1/∞ M4 and M16 with burst.
France AIF (competitors include HK 416 SCAR-L, ARX160A3, SIG 550/553, HS Produkt VHS-2) 5.56 S/1/∞ (not 100% certain. But the COTS rifles France has considered are all S/1/∞). FAMAS w/ S/1/3/∞. One selector selects safe/semi/auto, a second control makes auto 3 shots or full-auto
India Excalibur MIR (improved INSAS) 5.56 S/1/∞ INSAS w/burst/FAL/AK
Czech Republic CZ 806 Bren2 5.56 S/1/∞ CZ805 Bren w/ S/1/2 burst
UAE Caracal CAR 816 (AR-15/HK416 knockoff) 5.56 S/1/∞ Chinese Nationalist T91 w/ S/1/3/∞ and others
Finland SCAR-L 5.56 S/1/∞ SOF only.
Australia Thales EF88/F90 5.56 S/1/∞ F88 (Thales-built AUG) w/ S/1/∞
New Zealand MARS-L (LM&T CGB16) 5.56 S/1/∞ Steyr AUG A1 w/ S/1/∞
Turkey MPT-76 (HK417 derivative) 7.62 x 51 mm S/1/∞ G-3 with S/1/∞
Italy Beretta ARX-200 7.62 x 51 mm S/1/∞ Limited buy as DMR rifle
UK L129A1 (LMT LM308) 7.62 x 51 mm S/1 Limited buy as DMR rifle

There is one burst device which has potential, and that is a very high rate of fire burst, as configured in the never-deployed HK G11 caseless-ammunition rifle, and the Russian AN-94. In that type of mechanism, a slow, highly controllable rate of fire is used for full-automatic, user-controlled firing, but if “burst” is selected it’s delivered at a much, much higher rate of fire. The purpose is to use a small, dispersed burst to “correct” for aiming error by the shooter. As you might expect, even this burst device, which is potentially more practical than the usual type which cycles at the usual cyclic rate, is more of a mathematician’s delight than an infantryman’s.

Along with the definite decline of burst selectors, we also note that bullpups are also losing market and mind share. The Australians have gone with a new version of their bullpup, and France is considering replacing their bullpup FAMAS F1 and G1 with another bullpup (the Croatian VHS-2), but all the other candidates for the new AIF rifle are conventionally laid out.


  1. Source: Valpolini, Paolo. Small Arms. European Defense Review, Nº. 26., March/April 2016. pp. 19-26.