Category Archives: Weapons Technology

Kyle Defoor’s Range Gun “Inventory”

For the last week-plus, top instructor Kyle Defoor has been posting his “inventory” on his Instagram account, one a day. Our Traveling Reporter, a Defoor trainee and admirer, if not outright fan, has been linking them to us, one a day, and we’ve been waiting to assemble them and give you a single overview. Here it is; this is what’s in a single top instructor’s battery these days.

His training battery comprises eight guns, some used frequently and some for special purposes. There are four ARs (all BCM, which he endorses), two Glocks, one bolt rifle (Remington 700), and one DA/SA pistol (SIG 229 Elite). For each one, he painstakingly records the details down to the scope mount and slings and holsters, and he answers some reader questions, so for any gun that interests you, go to the linked Instagram page.

The AR Rifles

They’re all from BCM, with whom Defoor is in a committed relationship, as they say. BCM also provides the iron sights for those rifles that have ’em, and Viking Tactics (VTAC) the slings. There are a selection of calibers and lengths for specific purposes.

The most-used AR is this 11.5″ 5.56 mm Short Barrel Rifle (SBR), which is used 18-20 weeks a year for both military and civilian contracts.

The accessories include interchangeable red-dot and scope optics in Bobro mounts (Aimpoint Micro T1 and US Optics SR4-C respectively), the Streamlight Protac Rail 1 with an Arisaka Defense light mount, and a Gemtech flashhider for use with the G5T. The US Optics scope is their short-range 1-4 variable, which is presently off the market as the company overhauls its short-range line; its nearest military issue equivalent is the Elcan Spectre DR, which is not continuously variable. The SR4-C is an ingenious design, with a mil reticle (several options) on the first focal plane, which keeps the mils accurate with magnification, and a 4-moa red dot on the second focal plane. (There is an excellent five-part review of this scope at the Austin Police Marksmanship Team blog. Begin with Part 2 if you’re in a hurry; Part 1 is the justification for using a scope on a patrol carbine. Then click the left arrow to read subsequent parts).

Used 18-20 weeks a year for military contractcs and for some civilian carbine classes. My scope and Aimpoint share the same mounting slot on my top rail for ease of switching depending on what the customer wants.

Note that this is the baseline AR of a pro, and it’s run on an XM177-length barrel, probably suppressed more often than not. That’s a reflection of what’s happening in special operations units, not just in the US military, but worldwide.

Here’s a longer-barreled 5.56 AR used about 6 weeks a year for military and civilian scoped rifle classes. The barrel is 16″ stainless steel with 1/8 twist rifling and a mid-length gas system. The scope is a US Optics variable 1.8-10 power in a Bobro mount.

The Gemtech suppressor he uses with this rifle is the G5T; the rest of the accessories are the same as his other ARs.

Here’s a baseline .300 Blackout gun.  It’s got a 9″ button-rifled barrel. This one is used a few times a year for “specialized military contracts,” and is set up with a Gemtech flash hider for The One silencer.

What seems to be “the usual” KD4 accessories: BCM flip-up sights; VTAC Sling;  Aimpoint Micro T1 on a Bobro Mount; Streamlight Protac Rail 1 with an Arisaka Defense light mount. One thing this carbine has got that the others haven’t is a cleaning rod secured to the rail with zip ties.

And finally, this one’s just for hunting. It’s a 16″ .300 Blackout rifle with a 1/8 button-rifled stainless barrel, and has similar accessories to the other ARs.

The scope is the US Optics variable 1-4 power Dual Focal Plane on (what else?) Bobro. Kyle says he uses it to take deer, coyote and wild boar.

The Precision Rifle

This rifle is a modified Remington 700 with a 7.62mm NATO 20″ 1/10 heavy barrel, threaded for use with the Gemtech Sandstorm suppressor.

The mods/accessories include: a KRG stock and bolt lift; VTAC Sling; US Optics 1.8-10 variable power scope, with the Horus H25 reticle, mounted in Badger rings; and the ubiquitous bipod from Harris Engineering. Defoor uses it for military contracts 4 weeks a year.

I can’t express how happy I am with the KRG stock. It makes a stock 700 about .5 MOA tighter throughout the spectrum of the caliber compared to an OEM buttstock and is LIGHT! The weight thing matters when I’m humping long distances for FTX’s and evals. Additionally, KRG has accessories that are smart, lightweight, easy to install, don’t cost an arm and a leg and work WELL! This is expected from KRG since their owner is a mil snipe with experience like myself. I have no affiliation with KRG but if you’re in the market for anything bolt gun you should give them a look before they take off and get super busy,

Listen up to that recommendation, precision shooters: Defoor has a pretty good track record at flagging the Next Cool Thing before it gets cool.

The Pistols

The fundamental pistol of Defoor’s battery is the G4 Glock 19.

His regular carry gun is used for almost all classes, and apart from his own sights and his (Raven Eidolon) or Safariland holster, the only thing not stock Glock is the barrel, a KKM.

I’ve been using match barrels in Glock pistols for over 10 years now. I started using KKM’s somewhere around 2010 or 11 — long before it become the popular barrel of choice it is now. I also used Wilson combat match barrels for Glocks back when you had to fit them. I prefer hand fitting a barrel because I can make it even more accurate.

But he recommends you be in no rush to replace the barrel:

I tell everyone my opinion is to shoot the Glock pistol stock and wait to get a match barrel when you notice groups starting to open up a bit. In my experience this happen somewhere between 80 and 100,000 rounds.

In case you were wondering why Tier 1 units that shoot obsessively day in and day out went to the Glock, a lot of the answer is packed into that paragraph above. He also points out that the match barrel is match, not magic:

A match barrel will not help you magically shoot better all of the sudden. All it does is hone good fundamentals a little more. The average difference that I have measured over tens of thousands of shooters between a stock barrel and a match barrel at 25 yards on an NRA B-8 bull is somewhere between 3-4 points or around an inch tighter- both of these metrics are with a 10 round group from the standing unsupported position.

For about four weeks a year, for certain military contracts, he uses this older G2 G19, set up with a very unusual sight: an Aimpoint Micro on a Raven Concealment Balor mount. This one has had fewer rounds through it and still has a Glock barrel.

Sometimes he’ll just mount this slide on a G19 frame that allows a weaponlight or weapon laser. Same holsters; but he has some interesting observations on the Aimpoint vs. the more common pistol red dot, the Trijicon RMR.

If you want to go the route of a red dot on a pistol using an Aimpoint Micro will give you faster results in performance than an RMR. This is due to the Aimpoint being a tube and an RMR being a flat plane red dot. I’ve had great success and starting people off with a set up like this and then transitioning them to an RMR later.

I’ve assembled dozens of guns like this one for people who are older and whose eyesight just does not allow them to shoot irons affectively anymore — it’s amazing to see the reaction of people when they can shoot and perform the way they did 40 or 50 years ago. The Micro is definitely harder to conceal and will require some adjustments of clothing and belt type, along with a quality holster like mine. Safari land 6000 series holsters can be easily modified with a Dremel to hold this set up and still maintain retention. There are multiple reasons for MIL/LE to use this setup, although I recommend to all of our clients to issue two slides; one setup like this and one with traditional sights.

Sounds like we need one of these, or a trip back to the eye surgeon. (May not be an option. Our guy, the brilliant Dr Jack Daubert of West Palm Beach, has unfortunately had to retire).

Finally, there’s the SIG 229 Elite, which is used with organizations that use SIGs, or other DA/SA guns rather than striker-fired, and that don’t have a loaner gun for Defoor to use himself while conducting training.

Nothing magical here, just a pistol. About the only unusual thing here is that he got Raven to make him a one-off holster for the gun.

I also will sometimes use this when I’m training units that shoot a Berretta 92 when they can’t supply me with one (I don’t own a 92).

And that wraps up one instructor’s training and defensive battery. Instead of having many guns (either in quantity or in battery) he has stuck to basic platforms, and plowed his efforts into training instead. There’s a lesson in that if we want to pick up on it.


This post has been corrected. Kyle’s main go-to Glock 19 is a G4, not a G3 as we erroneously reported. We regret the error. -Ed.

Homesmithing News: Printed Revolver, Easy Home Rifling

Here’s the Imura Works’ latest Zig-Zag Revolver, the Flying Swallow. Imura Works is named for the Japanese martyr to the cause of home gunsmithing.

It has quick-change cylinders for rapid reloads.

Of course, this wouldn’t be that interesting if files weren’t available. But files are available — how ’bout that. The file pack includes not only the .stls that you need to print it out, but also assembly drawings that show how it all goes together.

Happy printing!

Beyond Printing: The Steel Rifled Barrel

Of course, a printed pistol has its limits; we’ve seen a lot of better examples of homemade guns made from steel. In an austere or denied environment, raw steel will always be available, but one stumbling block many small and home machinists have encountered has been rifling a barrel. But it turns out, there is a high-throughput, benchtop way to do it: electro-chemical machining (ECM). You don’t need a big ECM machine: you can improvise with innocuous parts and chemicals (table salt!). This is the whole setup:

Yep, the el cheapo battery charger is all the power supply you need. They used 33 AWG copper wire.

Here’s some results from an early series of experiments.

HERE it is! Rifling a barrel using the ECM (electrochemical machining) process by the one and only Jeffrod. This fosscad project is still in its early infancy so expect more to come! ECM is like reverse-electroplating where you are removing material instead of adding it. ECM is a very precise method and is more suitable for mass production. The ECM process can be used on hard materials that cannot be machined by other more traditional processes. Unlike the EDM (Electrical discharge machining) process, no sparks are generated with ECM between the cathode and anode.

That particular barrel used a pentagonal 3D-printed mandrel, copper wires, and three rounds of 5 minutes in a saline solution with 6 volts and 6 amps running through the wires. The rifling is 5-thousandths deep. It’s not a target barrel, but it’s a process that will produce a legal and likely functioning rifled barrel. And you can experiment with it with just some steel tubing, a bucket, wires and a mandrel. This is the mandrel, with the copper machining wires attached.

The whole process is recounted on this imgur thread, including several earlier experiments before this last barrel was produced. These barrels are a proof of concept, not in any particular caliber or chambering at this time. So we’re a long way from making, say, AR barrels, but a Sten barrel is close.

 You can’t ban guns. Make one problem difficult, and the community reacts to the damage by detouring around it. Short of lobotomizing the whole community, this is only going to grow from here.

New and Better ‘Nades in the Pipeline

It looks a lot like the M67 grenade, fielded during the Vietnam War to replace the M26, which in turn replaced the Mk2 of World War II. But in fact, the ET-MP (Enhanced Tactical Multi Purpose) grenade is a whole new thing. The differences from the M67 tell the story. It’s a little larger than a baseball-sized M67; it has a different fuze that lets right- and left-handed soldiers throw it the same way; and it is a selectable grenade that can be used as a concussion grenade (called “offensive” grenades in some armies) or a fragmentation (“defensive”) grenade. The user simply rotates a selector to the letter “F” (Fragmentation) or “C” (Concussion).

“Soldiers will not need to carry as many types of hand grenades,” Jessica Perciballi, project Officer the Enhanced Tactical Multi-Purpose hand grenade at the U.S. Army Armament Research, Development and Engineering Center, or ARDEC, said in a recent Army press release.

“They are currently carrying one M67 grenade that provides lethal fragmentation effects. With the new multi-purpose grenade, they can carry one ET-MP grenade and have the ability to choose either fragmentation or concussive effects desired for the situation.”

It’s weird to see a grenade fly without the spoon flying off, that’s for sure.

The effort marks the first time in 40 years the Army has set out to give soldiers a new lethal hand grenade. Warfighters lost the capability of using an alternate lethal grenade when the MK3A2 concussion grenade was taken out of service in 1975 because of an asbestos hazard, leaving the M67 fragmentation grenade.

Another feature is that the grenades are designed for ambidextrous use, meaning that they can be thrown with either hand. Current grenades require a different arming procedure for left-handed users.

The request for a multi-purpose grenade came from the warfighter in 2010, according to Matthew Hall, Grenades Tech Base Development lead. Research began almost immediately. The science and technology funding to move forward with a project came in fiscal year 2013.

“We received direct input from the Army and Marine Corps early on, which was critical in ensuring the new arming and fuzing design was user-friendly,” Hall said.

“With these upgrades in the ET-MP, not only is the fuze timing completely electronic, but the detonation train is also out-of-line,” Hall added. “Detonation time can now be narrowed down into milliseconds, and until armed, the hand grenade will not be able to detonate.”

via U.S. Army Working on a Dual-Mission Hand Grenade – Kit Up!.

The electronic fuze means it safely can do without the grenade “spoon” that was a feature of prior American grenades. The spoon worked as a grenade “grip safety” once the grenade’s pin was pulled, only allowing a hammer to fire a primer and start a chemical time delay burning when the grenade was thrown. That was why the M67 and its predecessors were designed for right-handed throwers, and awkward for lefties. (In SF, left-handed guys would often just straighten, remove, and reverse the grenade pin, which was all kinds of forbidden, but worked just fine).

The size of the grenade was determined partly by what they had to fit into it, but also by having real, junior soldiers handle dummy grenades, 3D printed in proposed form factors.

Likewise, the test troops, deliberately selected to be average and inexperienced soldiers from a cross-section of specialties, tried many different arming control designs, and provided their input before engineers selected the final one.

In addition to its human interface improvements and frag/concussion duality, engineers have also improved the stability and shock resistance of the grenades, allowing them to be stored and shipped more easily.

Steyr / Rheinmetall Enters the G36 Replacement Competition

At least three manufacturers are competing in the evolving process of selecting the Bundeswehr’s replacement for the unsatisfactory G36 individual rifle. The participants include H&K, SIG-Sauer, and Steyr, which is partnering with Rheinmetall. (Gun history buffs, Rheinmetall is huge now, but evolved from an ancient gunmaking firm… Dreyse, of Prussian needle-gun fame). Dreyse was based in Sommerda, but Rheimetall calls Düsseldorf home today.

G36: Los! (Out with it. Here a G36E clone).

The story is told at the indispensable German defense blog, Thomas Wiegold’s Augen Geradeaus! (“Eyes front!”). Our meatball translation:

On the standing theme of the G36 and future assault-rifle of the Bundeswehr, at year’s end we’ve got a new data point: Three German enterprises will compete for the provision of the new standard weapon for German armed forces. Along with Heckler & Koch, which already supplies the G36 and has had success with the HK416 in France, and the Eckernforde-based business SIG-Sauer, the German defense concern Rheinetall is stepping in — with a weapon from the Austrian manufacturer Steyr Mannlicher. The Austrians were defeated by Heckler & Koch in the competition for the new Bundeswehr rifle in the early 1990s.

(Thomas, if you read this, you’re welcome to use any part of our translation on your site, should you want to put up an English post. We know your English is good but your time is limited, and there’s great interest in the non-German-speaking world in the Bundeswehr’s decision process).

In any event, he goes on from there to quote from a story in the Vienna newspaper Kurier, which says that Steyr is developing an AUG successor called the Gewehr bei Fuß or Foot-Soldier’s Rifle. The model being offered to the Germans is called the RS556.

The Austrian journos think that Steyr lost back in 1994 because of politics — EU Brüderschaft be damned, German officials wanted German soldiers carrying German guns. With 60% of the value added in the manufacture of the proposed Bundeswehr RS556 version being Made In Germany, they think the away team has a better shot. Our translation of part of the Kurier report:

The Austrian weapons manufacturer already had a shot in Germany in 1994, when its legendary Steyr Universal Rifle AUG (Sturmgewehr 77) had the best result in tests, according to reporting at that time. Yet the German manufacturer, Heckler & Koch in Oberndorf, received the contract for 176,544 military rifles for its Sturmgewehr G36.

So what is the RS556? Essentially, it’s a reformation of the AUG’s technology into an AR-15 form factor. Indeed, at a distance, it’s hard to tell it from a SIG or a 416. So however this shakes out, the AR is going to notch up another win. From the same Kurier report:

The new RS556 indeed looks like an American weapon, but it is the further development of the Steyr Sturmgewehr 77. With just a handgrip and no tools the barrel can be changed. Ther eare three barrel lengths available, and the rifle can be employed as assault rifle, submachine gun or light machine gun according to length.

You may recall this was a selling feature of the AUG, although not one that seemed to be prized by end users. It looks like the Steyr RS556 is also fully ambidextrous.

Due to a special surface coating, the rifle also works without gun oil, which is an especially large advantage in desert operations. The gas system and the rotary-locking bolt are inherited from the earlier StG 77 (AUG).

The AUG had some success, arming Austria, Australia (in a local version; bad news for ill-educated Yanks who always confuse those entirely different countries), some of the UAE forces and (briefly, because nobody paid to maintain them) the US Immigrations & Customs Enforcement agency. (ICE now uses M4s in either semi or surplus configuration, which have mostly replaced the late lamented AUGs and the not-as-lamented MP5s).

When The Army Resisted the M16A2, Part 3 of 3

The previous two stories set the stage, for a look at a report drafted for the Army Research Institute for the Behavioral and Social Sciences the Army was still pursuing the “best” (an upgraded M16 meeting all Army objectives) instead of the “good” (the M16A2, which was developed and revised to meet Marine objectives). Of course, we all know the spoiler aleady: the Army accepted the Marine M16A2 as is, leaving the report as an orphaned artifact. The report is here:

Colt factory shot of the M16A2. The A2 was developed by the USMC, but was manufactured by Colt and FNMI.

This is the third of a three part series. In the first part, Thursday on, the Army contractors noted the specific solutions implemented on the A2 and the problems the Marines solved thereby, but complained that the problems and solutions were too USMC-specific. In the second part, posted yesterday, we discussed just what they thought was wrong about the Marines’ product. In this, third, part, we’ll list the modifications that they suggested in lieu of or in addition to the A2 mods.

Most of the Army’s problems with the A2 related to the burst mechanism, and the sights, especially the complicated rear sight. (This is actually an A3/A4 or M4: note the knobs, left, for removing the carrying handle. The A2 handle was forged as part of the upper receiver.


We should note that the Marines’ tests, as reported in this document (p,7), demonstrated significantly lower reliability, and increased fouling in the A2 compared to its older brother. These tests are suspect because the early lot of XM855 used was considered bad ammo, but the M16A1 did outperform the A2.

Thirty Ml6A1 rifles firing 26,010 rounds of M193

Failures to fire – none
Failures to feed – 3 (Not locking magazine in place)

Thirty M16A2 rifles firing 26,010 rounds of XM855

Failures to fire – 52 (27 – bad ammunition) (25 – mechnanical [sic] malfunctions)
Failures to feed – 3 (Improperly loaded magazines)

Those failures to fire that were not attributed to bad ammo were thought to be caused by the A2 trigger system’s Achilles’s heel, the burst trigger mechanism. The A2 performed even worse in a cold weather test, but again, it was with the questionable ammunition, and many of the failures to fire were also laid at the feet of the burst mechanism.

The report has an interesting discussion of the burst mechanism and its rationale in Marine, but not Army, small arms doctrine:

The M16A2 has less combat capability due to the elimination of full automatic fire. Full automatic fire enhances the ability of Army units to clear and defend buildings, to conduct final assaults on enemy positions, to defend against an enemy final assault, to conduct an ambush, to react to an enemy ambush, to engage an enemy helicopter or fast moving vehicle, etc.

While the Marines claim greater accuracy and conservation of ammunition for the 3-round burst control, no data were generated during the test to support these contentions and no supportative [sic] data are known to exist.

Also, it should be noted that room-to-room fighting was conducted with blanks, no close-in firing was conducted, no firing with short time limits was conducted, no firing at aircraft was conducted, etc. In other words, for all of the automatic/burst firing conducted during the test, a semi-automatic mode of fire would have probably resulted in a greater number of target hits.

Finally, to be given very serious consideration, is the fact that the burst control requires nine (9) new parts in the lower receiver, evidently contributing to the large number of weapon malfunctions during testing of the M16A2.

They also took issue with the heavy barrel (“heavy in the wrong place”), the twist rate (preferred 1:9), stock length increased when even the A1 stock was too long for small soldiers, and the fast twist’s incompatibility with the .22 subcaliber system. 

The article includes an extensive comparison of the pros and cons of Marine KD vs. Army Trainfire marksmanship modalities. These training differences result from the different combat envelopes for the rifleman: the Marines need to engage with rifles in the 300-to-800 meter space, because they don’t have the supporting arms that the Army can count on, at least, not in the same quantity. A unit that must fight with just its organic weapons needs to get the very most out of these weapons. The Army of 1986 did not consider a 500 or 600 meter target a primary rifle target, but a crew-served-weapons target.

In the end, the recommendations the contractors made were mostly about the sights. They put their recommendations in a table with the M16A1 and M16A2 stats. Since the latter are probably familiar to most readers, we omit them now to save time, and just show the contract recommendations.

Item Recommended
Front sight (day) Fixed blade, 0.090″
Front sight (night) Luminous dot on each sightguard
Rear Sight (day) single 2mm peep. A single elevation knob marked for 200, 250, 390, 25, 400, 500, 15, 600, 700, and 800 meters. Windage knob at rear. Each click equal to 1 MOA
Rear Sight (night) Two luminous dots on upper portion of receiver (or a single flip- up luminous dot located forward of the carrying handle) are aligned with front dots for shooting at night
Zero Recording Yes
Zero Inspection Yes
25m setting (day and night sights) Yes
Mechanical Zero Yes
250-m battlesight Yes
Firing mode Semi and Auto
Barrel 20″. Slightly heavier than A1 at receiver and mid-barrel. 1:9″ twist
Handguard Same as M16A2 except held in place with a securely fastened ring nut to provide rigidity.
Buttstock Same material as M16A2. Same length as M16A1. Option for adjustable length.

There are several interesting observations to make here. First, the contractors recommended that the Army make changes that would decrease the mechanical accuracy of the proposed M16Ax relative to the Marines’ A2. Specifically, these changes included the wider fixed front sight blade, the 1-MOA adjustments on the rear sight (A2 offers ½-MOA), and arguably the simplification of the rear sight. The trade-off was simplicity and ease of training, instead of superior bullseye performance.

Second, some of the proposals would definitely improve the utility of the firearm, including restoring the short stock, or replacing it with an adjustable one; increasing the barrel diameter towards the chamber rather than the muzzle, thus improving sustained fire accuracy and reliability; reverting to automatic fire from the burst mechanism (which also has side benefits, in improving the trigger’s feel and consistency). The night-sight proposal was truly ingenious.

Third, in some of these road-not-taken proposals, the Army was reverting to the original AR-10 design and rejecting changes that were largely imposed on the AR design by the Army in the previous decade. These include the rigid fastening of the handguard, and the fixed front sight blade.

Finally, these proposals were almost the last gasp of the iron-sighted military rifle. As this  document passed from the contracting officer to file cabinets across the service, without action, special operators were already wringing out scopes and single-point sights, and a few visionaries were already arguing that the day of the iron sight had run its three centuries, and was now at an end. A new generation of optical technology was eliminating the two objections that had kept optics off the rifles of most soldiers: less durability than irons, and slower target acquisition. Many men’s efforts went into winning over the Voices of Experience who still said “no” to anything with a lens, thanks to memories of Uncle Joe’s elk lost because his scope fogged up, or the VC that got away because somebody attached an unauthorized 4×32 Colt scope to the carrying handle of his M16.

When the Army Resisted the M16A2, Part 1 of 3

The M16A2 was adopted by the Marines in 1983, and then by the Army three years later, but all of its development was done, largely on a shoestring, by the Marines.

For example, the finger bump on the A2 pistol grip? The very first prototype was built up by a Marine officer on an A1 grip, using plastic wood or body filler! Most of the modifications to the A2 were aimed at:

  1. Increased practical accuracy;
  2. Increased effective range;
  3. Increased durability; and,
  4. NATO compliance (adopting a NATO round equivalent to the FN SS109 round).

In a brief overview of the service life of the M16 series for American Rifleman in June, 2012, Martin K.A. Morgan encapsulated this history well:

In November 1983, the U.S. Marine Corps adopted a product-improved version of the M16A1 chambered for the 5.56×45 mm NATO round. The new rifle was called the M16A2 and it differed significantly from its predecessor: improved rear sights, a brass deflector, a heavier barrel and 1:7-inch rifling were among the changes. The M16A2 also replaced the M16A1’s “AUTO” selector setting with a “BURST” setting delivering three rounds with every trigger pull. The Army followed the Marine Corps’ adoption of the improved rifle in March 1986 when it ordered 100,176 M16A2 rifles from Colt. In September 1988, the U.S. government placed an initial order for 266,961 M16A2s with Fabrique Nationale’s North American subsidiary, FN Mfg., Inc. of Columbia, S.C. Late the following year, when 57,000 U.S. military personnel conducted the Operation Just Cause invasion of Panama, the M16A2 was used in combat for the first time.

For practical accuracy, the A2 had new sights, with a square front post; for range, a new round with a heavier bullet, and new rifling to match; and for durability, new stocks and handguards and significant metal reinforcement in the lower receiver’s weak areas, the pivot pin bosses and buffer tower.

The rifle was not without controversy in the Army. Indeed, contractors for the Army Research Institute for the Behavioral and Social Sciences examined the rifle and concluded that, as their paper’s abstract notes:

[U]se of the M16A2 rifle by the Army would be extremely problematic, a-fact due, in part, to the vast differences between the marksmanship training philosophies of the Army and the Marine Corps.

(The paper is here:

The Army had been researching improvements to the M16A1 for years, but hadn’t actually implemented any. In the foreword to the Army Research Institute paper, the word “problematic” crops up again and one gets the sense that the problem was this solution was Not Invented Here, and moreover, not developed the way the Army wanted to develop one. 

Referring to earlier research, they wrote:

A detailed evaluation of M16Al performance was conducted to determine adequacy, peculiarities, etc. The findings clearly indicated that the M16Al was an adequate combat rifle; however, many shortcomings were identified that should be addressed in a new rifle or any rifle Product Improvement Program (PIP).

They considered that the improvements in the A2, listed below, were suitable only for the peculiar circumstances of Marine Corps service.

The Marine Corps test results stated the following advantages for the PIP [Product Improvement Program -Ed.] rifle:

  • Ease of training (handling and ease of sight movement).
  • Improved safety (no hazard when adjusting elevation on the rear sight even with loaded weapon).
  • Increased effectiveness at long ranges (more hits, better accuracy, and greater penetration).
  • Improved handling characteristics and durability in hand-to-hand close combat.
  • Reduced barrel jump and muzzle climb during automatic and rapid fire.
  • Increased contrast and less glare with square front sight post.
  • Stronger, more durable and improved grasping characteristics of front handguard.
  • Stronger barrel with quicker twist to take advantage of increased effectiveness provided by new ammunition.
  • Improved sighting characteristics providing quick target acquisition for moving targets and better detection of targets in low level light conditions at close ranges, and more accurate long range fire by use of two modified rear sight apertures.
  • Increased ammunition conservation and more effective use of ammunition with burst control device.
  • Conformity to human factors standards by lengthening stock (alleviating bruised eyebrows, noses, and lips).
  • Stronger, more durable stock.
  • Stronger, more durable buttcap which also reduces slipping on the shoulder during firing.
  • More controllable and comfortable pistol grip contoured to the shape of the hand.
  • Improved brass deflector which protects left handed shooters from hot ejected brass casings.
  • Can use NATO type improved ammunition (XM855) which provides improved performance and penetration at long ranges.

The Army evaluators were impressed by that list of solutions, but thought they all traced back to four specific USMC objectives or requirements:

The above list of advantages is very impressive. It appears that the rifle meets the primary requirements stated by the Marines:

  • A sight adjustable to 800 meters.
  • A bullet with better accuracy at 800 meters and the capability to penetrate all known helmets and body armor at ranges of 800 meters.
  • A rifle with more durable plastic parts and barrel which will take a beating during bayonet training and extended field exercises.
  • The replacement of the full automatic capability with a burst mode which fires a maximum of three rounds with each pull of the trigger.

…but they thought that the requirements were too Marine-centric.

The list, however, represents the objective and subjective evaluation of Marine Corps personnel who are emphasizing the most positive aspects of rifle characteristics as they pertain to envisioned Marine Corps requirements.

This is the first of a three part series. In the second part, tomorrow on, the Army contractors damn the A2 with faint praise and list a litany of A1 shortcomings that they believed that the A2 did not resolve. In the third part, the modifications that they suggested in lieu of or in addition to the A2 mods are enumerated.

As it was, the contracting officer’s representative approved the paper in February, 1986. In March, and probably before any of the responsible officers read the paper, the Army went ahead and adopted the M16A2, just the way the Marines had shaken it out.

That makes this paper a time capsule.

Twists of Fate, and Rifling

What separates the winners from the losers is how a person reacts to each new twist of fate.  -Donald J. Trump.

We’re not sure about twists of Fate, but a number of you have asked us about twists of rifling. The question usually comes in the context of AR-15 rifles and their clones, with rifling twists of 1:14. 1:12, 1:9, 1:8 and 1:7 all having been used.

Can you calculate optimum twist for a given caliber and projectile? Yes, you can. There are two equations that are commonly used, Greenhill’s and Miller’s.  Let’s start with the newer one, Miller’s, which was originally proposed in Precision Shooting in March, 2005:

Miller assumes a spitzer-pointed, boat-tailed projectile. In Imperial measurements:

T is twist
30 = a constant representing: standard atmospheric conditions, and a bullet speed of approximately Mach 2 (2800 fps at sea level in standard atmospherics). If you need real precision, Miller does provide more complete equations for that, but these approximations work for rifle velocities.
m = projectile mass, decimal grains
s = gyroscopic stability factor
d = diameter, decimal inches
l =  length in calibers (i.e. length is “l” times the caliber of the projo).

Greenhill’s rule dates originally to 1879, and is frequently used by gunsmiths as it is (or was. anyway) taught as part of gunsmithing school, repeated in Hatcher’s Notebook, and included in Patrick Sweeney’s rifle gunsmithing book among many others. Sir Alfred Greenhill of the Royal Armories at Woolwich developed a number of more complex equations. (More complex than Miller’s, too). But he also provided “Greenhill’s rule of thumb.” Sweeney describes this as follows:

“The length of the bullet in calibers, multiplied by the twist rate in calibers per turn, is 150.”

The constant 150 is good for velocities to about 2800 fps. For higher velocities, as often seen with small-caliber rifles, use 180.

Some notes on twist

As a rule of thumb, the more twist, the more stable the bullet. A bullet must meet a threshold of stability to be accurate. The less twist beyond minimal stability, the less accurate the bullet, in theory, but practical accuracy doesn’t drop off until a bullet is very overstabilized. In small calibers, varmint hunters will tell you a too-fast twist will cause bullets to self-destruct from centrifugal force before overspin hurts their accuracy.

You also need enough excess stability to account for atmospheric changes. As a rule, air density decreases with increased altitude above sea level, and air density decreases with rising temperatures. Less dense air needs less spin than more dense air. This is why the original AR-15 prototypes were found to lose accuracy during Arctic testing by the Air Force — important tests for guys who might have to defend ammo igloos in Iceland, antennas in Alaska, or missiles at Minot. These prototypes had barrels made by Winchester for Armalite in 1:14 twist, then the standard .22x varmint-rifle twist (no one pops prairie dogs in -20F weather). A change to 1:12 solved the problem, at least, for 53-55 grain bullets like those in what would become M193 ball ammunition. (Lighter weight tracer rounds have always been hard to stabilize and trajectory match in 5.56mm). The change to 63 grain ammunition drove the change to a 1:7 rifling twist.

These same calculations may not scale to all types of large-caliber, high-velocity artillery pieces such as tank guns. That’s because air is not truly dimensionless; air molecules don’t scale up as projectiles do. Aerodynamicists and exterior ballisticians can compensate for this scale effect by incorporating Reynolds Numbers in their calculations. For rifle ammo, it’s not necessary or useful.

For those who just want a cheat sheet

Simplified from Sweeney, Gunsmithing Rifles, pp. 109-110

5.56 and other .22 centerfires:

Bullet weight grains Twist ratio 1:inches Velocity
> 70 8 any practical
≤ 70 9 any practical
≤ 63 12 any practical
≤ 55 14 any practical
≤ 55 15 ≥ 4100 fps
≤ 55 16 ≥ 4300 fps

Note that this is really for civilian use in “normal” climactic conditions. For military purposes where you must meet a +140ºF/-40ºF standard, you should go one twist increment slower per bullet weight increment, and understand that you will lose some ability to use weights at the extremes removed from your selected optimum round. Not much of a factor in a military application, where the fewer different DODAAC codes (ammunition stock numbers), the better, as far as the logistics elements are concerned.

7.62 NATO and other .308 centerfires:

Bullet weight grains Twist ratio 1:inches Velocity
> 220 8 any practical
≤ 220 9 any practical
≤ 170 12 any practical
≤ 168 14 any practical
≤ 150 15 any practical

Note again that this is for civilian/sporting/normal-climactic-conditions use.  And that it applies to supersonic rounds only. You must redo the calculations for the slow, heavy bullets used in suppressed applications!

For those desirous of plug-in calculators:

For those desirous of more sheet music:


3d Printed 1911 ( in .22LR Caliber)

It’s been a long time since we’ve done any kind of 3d Printed Guns update, and things are still proceeding at a staggering rate, with lots of interesting gun designs and also a real explosion of accessories.

However, here’s something everyone seems to have been anticipating: a working 3DP M1911. Except… it’s only working in .22, so far, it’s not working 100%, and as we’ll see it took several iterations to get there.  The developer goes by the name MBA Firearms. This is the current iteration:

In an Imgur album, the poster says this:

Here it is, the FIRST EVER 3D-printed 22lr semiautomatic pistol. These 1911 models were printed, assembled and test-fired by MBA. There are many firsts with this gun. This design is still in development but improvements are being made.

It’s not a very high round-count gun yet.

95rounds of .22lr through the latest model. Getting light primer strikes about 1/3rd of the time because I lightened up the mainspring too much.

Several different materials were used on developmental frames.  The upper is a .22 Kimber conversion kit. 

Changing to 910 reduced warping of the rails. The warping was partly due to the weight of the mainspring. Tests with 15# spring worked well but was obviously to light leading to light primer strikes. More testing will be done with 16# and 17# spring later which are ready to go.

The reference to 910 is to Taulman 910 nylon filament (the spool is visible). It’s strong stuff, but needs to be kept dry aggressively as possible, and may need higher temps that some printers prefer.

This image above shows the characteristic layering of 3D printing on consumer printers. The next picture shows four of the test frames. The one that’s built up into the gun is made of Taulman 910.  The white one is made of ABS. The ones that have “attached” grips actually had the grips molded in as part of the pistol.

This is the first functioning 1911 we’re aware of, to have been built on a consumer 3D printer. As such, it is a milestone of considerable significance.

Here’s the initial design and test-firing video.

And here’s a follow-up with more test firing. Better, but still not reliable.

Five Thoughts on Firearms Design

We’re very, very busy right now, and so we’d just like to throw some gun zen at you, maybe to be elaborated later.

I: The safety never breaks on a Tokarev TT-33.

II: Anything good enough gets copied. The better it is, the faster it spreads.

III: German engineers love complexity above all. It’s a natural characteristic.

IV: The most successful guns are not just functional, but beautiful also. (Perhaps it helps them sell. Even military designs must attract boards of officers). Most failures are ugly.

V: Over time, good designs drive out bad. This drives consolidation until there are new breakthroughs, in a process of punctuated equilibrium.

Even Glocks Can Break

even_glocks_breakAnybody recognize this little bit? If you run a Glock you probably do.

It’s the thumb button from what people trained on 1911s or other classic firearms tend to call a “slide release” and what Glock insists on calling a “slide stop.”

Why does Glock call it a “stop” and not a “release”? You’re looking at the reason. The cheap stamped part is not designed or manufactured to take the load of being used to release the slide. Official and canonical Glock practice is that you close the slide on a fresh mag by pulling it to the rear and letting it go — like a Luger or P.38, not guns that have Browning’s handy slide release. 

Of course, the slide release of a 1911 or BHP is machined from steel billet and heat-treated appropriately. JMB Himself intended you to mash your opposable thumb down on it to close the slide, because you needed your left hand to manage the reins of your cavalry mount anyway!

This image comes from Kyle Defoor’s Instagram, where he says:

Seeing some military and LE Glock 19 Gen 4 slide stop levers breaking more than a few times. Never seen this before so often.

A lot of his commenters are… well, we’re not willing to trade commenters with him, let’s just say that. But one of them had this observation, which gibes with what we’ve heard about Glock training.

I’m a factory certified Glock armorer and at my last recert they discussed their position that the slide stop is not a slide release and using it in this fashion can, over time, lead to failures.

And couple more had the sensible comments that,

If not a slide release why the ridges on face for grip?


It seems to me that it would get more abuse from going into slide lock than slipping out of the notch to send the slide foreword again. What am I missing?

To which the Glock armorer guy replied:

[T]hat’s a valid point and an acute observation. I am remiss in failing to ask my Glock rep, who was in my office just yesterday, for clarification on this.

OK, let us offer our own opinion (note, opinion) on this.

  1. In our opinion, the “don’t use it as a slide release” is a retrospective position that was created by the Glock organization ex post facto when someone broke a slide release. But the oldest official Glock documents we have on hand (a January, 1992 armorer’s manual, and a Glock G1 exploded view dated 1991) already refer to the part as a “slide stop lever.” (The part owners often call a “takedown catch” is, officially, a “slide lock,” not to be confused with the slide stop lever).
  2. Re: “why the ridges on face for grip?” On p. 14 of the 1992 armorer’s manual, it describes how to lock the slide back, and includes a picture. “[L]ock the slide open by pushing up on the slide stop lever while pulling the slide to the rear with the non-shooting hand.” (It then tells you to “Pull back slide to release slide stop lever and close action.” But it doesn’t warn you not to use the slide stop lever to release the slide).
  3. “Why does it break?” OK, here’s a couple pictures of Glock slide stops. First, here’s an OEM slide stop, photographed from the inside. glock-oem-slide-stop-insideNow, we didn’t have a handy photo of this from the outside, but this photo of a Vickers Tactical extended slide stop (we’ve got this part on our own Glock) shows what the other side looks like. glock-vickers-slide-stop-outsideCompare this to the failed stop at the top of this post.

We now have several clues as to why the stops are failing.

  1. People continue doing something the manufacturer says not to do.
  2. The slide stop is made from a single piece of sheet metal, stamped (“pressed” for Europeans) and folded to net shape.
  3. There is a small rounded notch, adjacent to the part of the stop that folds over to the inside, right where the part Kyle photographed began to fail (see where the failure crack is kind of gray at the top? That’s the oldest part of the failure. When it weakened the slide stop enough, the rest failed all at once — that’s the shiny part of the crack). The reason for the notch is to prevent a “stress riser” from causing the part to begin failing at this point, and it obviously is not working in 100% of use conditions.
  4. And that the problem just started showing up with greater frequency, suggests that some aspect of the manufacturing of the part may have been changed recently. Manufacturers are always making small changes in parts to improve something about them (often something that matters to the manufacture, like lower cost, or increase speed of manufacture, and doesn’t matter quite as directly to customers). Manufacturers also are known for making parts in-house and outsourcing other parts to subcontractors. These subs can change at any time.
  5. Putting thumb pressure on the slide stop stresses it several different ways. It can load it in torsion (twist), for which the engineers probably didn’t do the math on this part. It will definitely bend the part laterally (per the gun’s orientation). That stresses the outboard (left) side of the slide stop in tension, and the inboard (right) side in compression. Another way to think about it is when you bend a plate or bar, the side bent convex is loaded in tension, and the side bent concave is loaded in compression. Our best guess (and based on one picture of one part, it can be no more than a guess) is that this part began to fail from tension at the upper outboard corner of the slide stop.
  6. It’s a trivial physics or engineering problem to calculate the stresses on the part, but to know whether they exceeded the design strength of the part, we’d need to know the exact materials and heat-treating condition of the part.

A question on the Instagram page about whether this is happening primarily in high round-count guns isn’t answered, but round count doesn’t necessarily load the slide stop. A lot of cop guns are seldom fired, but are loaded and cleared at least once every shift. If they’re thumbing the slide stop a lot, they can bust their slide stop without even firing a shot.

One last thing: the failure of this actuating button end of the slide stop makes it impossible (or very difficult, requiring tools) to lock the slide back without an empty mag in the pistol. However, without the end of the stop, it looks to us like the basic running of the gun would still be OK, until you needed the slide stop to handle a malfunction. So in combat terms, this failure of the slide stop is fail safe.