Category Archives: Industry

Another 3D Firearm Approach: Plastic Casting

Here’s the situation: say, you want to test a new firearm or part design, and because you’re iterating rapidly, 3D printing would be ideal. But the mechanical properties of common 3DP polymers, polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) are insufficient, and it’s either more challenging or more expensive to print in materials with better mechanical properties, like nylon.

Lost PLA 10-22 receiver. The casting with filler and riser still attached.

Lost PLA 10-22 receiver. The casting with filler and riser still attached.

One answer, that we’ve covered before, is to use Lost PLA casting. (Indeed, industrial specialty printers are made for printing in wax for the very similar process of lost wax casting; small ones are widely used by jewelers, and at least one major investment-casting supplier to the firearms industry uses a pair of large ones every day). But while you can 3D print in your office or kitchen, metal casting requires working with a great deal more heat, and molten metal. And casting itself is a complex knowledge domain with lots of things to go wrong and a wide gulf of tribal knowledge between the amateur and today’s professionals.

So we give up, right?

Nope. Wrong. There are still several technologies open to us, like metal injection molding (which probably made the fiddly bits inside your carry handgun, unless you’re old school). But even that has some complexities, even though it shows signs of integrating really well with 3D printing. Basically, you can do the prep work, but someone with an industrial setup needs to do the actual MIM for you.

How about plastic casting? There are plastics that are a pain to 3D print, but that can be cast at room temperature and atmospheric pressure. Fosscad experimenter FP gave it a shot, and produced some gratifying results: plastic AR lowers that appear to be superior in strength to 3D printed versions.

The difference between plastic casting and plastic injection molding which is how your Smith or Glock frame is made is that injection molding is done under pressure, and casting is done in atmospheric conditions. That means that casting will usually be less dense and will be done with materials that are poured and set at lower temperatures, as a rule of thumb. Molding is commonly used on Hollywood sets and props, for example, but it also has architectural and industrial applications. Both the silicon “rubber” for the mold and the plastic for the castings come in parts that react and solidify when mixed.

Mold silicon and casting plastic

This page on imgur walks you through two complete batches of plastic casting multiple AR lowers using two different molds, one contained in a see-through plastic box and one in a wooden box.

The sequence of events is:

  1. Print and prepare (i.e. strip off support material, acetone-vapor treat, etc.) your lower or other master part (called a “pattern” in casting).cast plastic -- 3DP pattern
  2. Prepare a mold box and place your pattern in it. Include some material to form a pouring inlet, runners or sprues if needed, and an air release hole.cast plastic lower - mold box 1
  3. Prepare and mix the mold RTV and pour it into the mold box. Let it cure. Beware of exothermic reactions.cast plastic lower - mold box
  4. Once the mold has fully set, remove it from the box, and carefully cut the silicone away from the pattern, taking care to neither damage the pattern (you may want another mold; they don’t last forever) nor, especially, the mold.  Cut apart, the mold will have four parts: left, right, bottom, and core. cast plastic lower - pattern out of mold
  5. Reassemble the mold in the mold box.
  6. Mix and pour casting plastic; let it set.
  7. Open the mold and remove the cast lower. cast lower - out of the chrysalis
  8. Repeat as needed.

Initial testing suggests that these lowers are stronger than printed lowers, and there are stronger, more exotic casting plastics available. Some of this testing has already begun. Here’s a lower cast in “Simpact 85A” showing off its ability to be bent 90º and snap back to original position — probably not useful as an actual gun, but could be a stage or stunt prop.

flexible simpact lower

Next week we’ll show you some impact tests of different printed and cast lower materials, done by “Freedom Printing 3D”. These bear out the supposition that some plastics are much stronger than others.

More testing is required to determine the number of cycles the molds can bear before they begin producing out of spec parts.

Some suggestions moving forward.

  1. Rather than cut the mold open after pouring it around the pattern, use mold release compound and a cope, drag and core system to make the mold so it can be disassembled without drama. This would make for faster mold-making. But only testing will tell if this makes a good-enough mold, or if the cut-apart kind is dimensionally/structurally superior.
  2. While using a printed lower is convenient because it’s easy, and it’s also a lower design already modified to strengthen a weaker material, you could use this system on a lower carved by hand.
  3. You could even use this system to duplicate a factory aluminum lower, but the plastic almost certainly won’t be strong enough in what we’ve learned are the AR’s most vulnerable areas: buffer tower, pivot pin bosses, pistol grip boss, and trigger guard “ears.”

Judge: 3D Gun Files Will Start a War, and Justify Dropping Bill of Rights

Digital files for the Liberator pistol have been ruled a casus belli by an anti-gun judge.

Digital files for the Liberator pistol have been ruled a casus belli by an anti-gun judge.

We mentioned Defense Distributed’s case against the Department of State last week, not knowing that an initial document was about to drop from the judge. The document has dropped, and we won’t sugar-coat it: it’s not good.

Here’s the story at 3D (complete with a dose of anti-gun editorializing, slant and dishonesty from writer Scott Grunewald1et tu, and here’s the injunction denial at Scribd. It has also been added to the documents at Defense Distributed’s legal page.

We also host the denial here, for those of you nervous about going to a page associated with Administration target Cody Wilson:


The judge’s opinion shows his anti-gun bias, for example when he suggests that availability of firearms information is a cause of war:

Defense Distributed admits its purpose is “facilitating global  access to, and the collaborative production of, information and knowledge related to the three-dimensional (“3D”)printing of arms.”  Facilitating global access to firearms undoubtedly “increase[s] the possibility of outbreak or escalation of conflict.” Defense Distributed,by its own admission, engages in conduct which Congress authorized Defendants to regulate.

The judge does two things here. First, he equates “access to… information and knowledge” to “access to firearms.” That is like saying that having Das Kapital in the library is equivalent to perpetrating the Katyn Massacre. Then he suggests that providing this information causes wars. By this succession of mountain-goat logical leaps, propelled entirely by bad faith, he gets from providing information and knowledge”  to the conduct the State Department is allowed to regulate, the very different “increasing the possibility of outbreak or escalation of conflict.” 

The game is not over yet2; we’re just in preliminary injunction stage, and an injunction is hard to secure. But the judge, Robert Pittman, has telegraphed that his sympathies are entirely with the Department of State, and that he considers both the first and second Amendments to be dead letters, mere junk DNA in his ever-evolving Living Constitution, and having no weight against the decree of an unelected, unaccountable bureaucrat.

This is far from the only issue with Pitman’s opinion; his 2nd Amendment analysis marshals a number of cases to render the amendment a dead letter, and he similarly dismisses the 5th Amendment as having zero weight wen balanced against a bureaucrat’s preference.

By Pitman’s reasoning, and by the State Department’s, this entire blog is an export and a violation of law.

Pitman, a liberal, anti-gun Democrat, received his judicial appointment from President Obama a few months ago as a reward for political loyalty as a US Attorney, a political contributor, and a gay-rights activist. As US Attorney for San Antonio, he ran a partisan shop that made prosecution decisions on racial and political lines, and at times joined in racial-quota cases. As a judge, his decisions have broken entirely on partisan lines; for instance, in June he swept away a challenge to new NLRB rules that rewrote the law to erase employee privacy and require their contact information be disclosed to union organizers.

Getting a fair trial from this judge is not going to be possible, and the plaintiffs are probably going to have to plan for a battle that encompasses an appeals fight. That means they’re going to be more dependent than ever on our support.

In addition to the vital court fight, We the People, to use another archaic phrase deprecated in the law library of  have a way of cutting this negation of the first two items in the Bill of Rights off at its bureaucratic knees: we can appeal to Congress.

Yeah, we know. Not an ideal position to be in, between a judge who worships bureaucratic Authoritah and a bunch of Student Government nerds grown arrogant in the corruption of their power, but that’s where we are. Before we approach Congress, we need to know what we want, and how to operate the only two levers that move a Congressman (bribery and fear) to bend them to our will.

For More Information

Here are two stories with some of Cody Wilson’s, and his co-plaintiffs the Second Amendment Foundation’s, reactions also.


  1. Since Grunewald’s a liar, we expect him to lie about this, too. But he wrote: “The 3D printable AR-15 rifle receiver allows a standard AR-15 to be modified to shoot larger, more destructive ammunition.” It does no such thing, of course. Grunewald just made that up.
  2. “Was it over when the Germans bombed Pearl Harbor?” — Sen John Blutarsky.

How NoDak Spud Polishes an A1 Lower

Here, in real time, NDS’s very efficient Mike polishes one of the company’s outstanding retro lowers. Polishing is necessary before blasting, which is done before anodizing, to allow the anodizing to take evenly and not be blotchy.

NDS is an interesting combination of idea, work ethic, and customer service. You get straight talk, no bull about ship dates, for instance. If they discontinue a product, like their unique “605” upper receiver that cloned modified M16A1 upper forgings that imitated some tens of thousands that were used briefly — and with permission of the Contracting Officer and Contracting Officer’s Technical Representative — to substitute for short-supplied “slick-side” forgings for USAF M16 rifles. (They discontinued it because they were a ton of work for a slow-selling product).

As Mike notes, it’s a small company. Call or email them and you’ll probablt tallk to Harlan, maybe Mike, and when you see the quality of their parts, you’ll be calling back. Almost every customer is a repeat customer. We’ve lost count of the number of NDS lowers we’ve bought (whoever the guy at ATF is that keeps the N-Z section of The List probably knows) but we think we’ve bought six different kinds. 

And, oh yeah, they make AK receivers, which are the class of the field, and a replacement for the crappy plastic AR-18S lower.

To order or look at their product line:

Large-Scale Clandestine Production of Small Arms

There are a number of designs out there for “resistance” type submachine guns that circulate on the net and are available in books. Many are familiar, for example, with P.A. Luty’s Expedient Homemade Firearms: the 9mm Submachine Gun that landed Luty in hot water with Scotland Yard, or with the work of Bill Holmes (a pseudonym); many of these books date from the golden age of the survivalists in the 1970s and 1980s.

These books are not as far-fetched as you might think. In World War II, the open-bolt submachine gun was found to be well adaptable to converted automotive-part and -accessory production lines (in the form, for instance of the M3 and M3A1 submachine guns) and equally well adaptable to cottage industry (in the case of the Sten Mk II). Resistance organizations built their own submachine guns, often modeled on airdropped Stens but sometimes of indigenous design, such as the Polish Bljeskavicza (sp?).

Resistance groups that produced Sten copies included the French, Norwegian, Yugoslav and Greek resistance, and a number of these home-grown subguns grace those nations’ museums. In an unusual twist, Germany produced its own Sten copies of several types (the most well-known being the MP 3008) during its in extremis phase.

In the 1960s, an American went to prison for supplying counterfeit Stens to Cuban exiles for their war on Castro’s socialist workers’ paradise.

One of the books that offers plans for an open-bolt submachine gun derived from Uzi, CZ 23-26 and Sten practice is Gerard Métral’s (an obvious pseudonym) Do it Yourself 9mm Submachine Gunpublished in 1985 by Paladin Press. The meat of Métral’s publication is sixty-odd dimensioned drawings of parts, which if fabricated and assembled would produce a crude 2nd/3rd generation open-bolt submachine gun, but he also addresses clandestine serial production, as opposed to the one-off manufacture of hobbyists. Here’s an extract of that bit of his book:


These basic principles can be explained by the following joke, believed to have been originated by Jews in Palestine during the last months of the British mandate.

A poor man was working in a plant named Sewing Machines, Inc. He wanted to give to his wife a sewing machine but had no money to buy one, so every evening he’d smuggle home a different piece that his factory was making.

After many days his home stock was complete, and he tried to assemble the machine for his wife. He tried many times, but he always ended up with a machine gun.

A clandestine resistance organization needs considerable quantities of weapons. The importation of complete guns may be difficult and costly, and a single police operation may undo months of effort.

Such an event happened to the Irish Republican Army, when on 30 October 1987 the Eskund II, a ship loaded with tons of Libyan weapons was intercepted by the French authorities. The method suggested here consists of a decentralized mass production of harmless metallic pieces that may be used for various purposes. All machining operations requiring heavy machine tools are completed at this stage. The parts are then dispersed in several small workshops where they can be completed without special tools or skilled labor.


The clandestine organization needs efficient cover to buy large quantities of metallic components without alarming the authorities. The only way to do this is to control at least three small or middle- sized industrial plants used for subcontracting work and with a regular output of some kind of mechanical devices.

You must have a net of interconnecting enterprises devoted to the decentralized production of mechanical devices. The idea is that the orders and movements of the gun components will be completely hidden in a stream of civilian goods.

It is also assumed that you observe all the basic rules of security for a clandestine organization.


Many components of the submachine gun could belong to any civilian mechanical device, and no one would likely suspect their final destination, at least in their half-finished state. I call these elements “general-purpose pieces.” The clandestine organization may order them from ordinary factories. The springs used in the gun are good examples of such pieces, as are the plugs and support rings.

Salami-principle sear

Salami-principle sear from partially-prefabricated bar stock.

Other components are to be made in two steps. First a bar is machined to the correct profile in an industrial factory. The longer the bar, the better the camouflage. These bars are then dispersed to the smaller workshops, where they are cut like an Italian salami. Most of the resulting rough cuts require only a few drillings to finish the piece. I call these parts “salami-principle pieces.” The sear, the bolt, and even bolt carrier are such pieces.

The receivers and trigger mechanism housings are taken from commercial steel tubes and U iron, which appear innocuous. Once the work has begun, it will be difficult to conceal the parts’ ultimate function. Fortunately, this phase is done quickly, even in small workshops. For your security, you must remove the pieces from the workshop as soon as they are machined.

The pistol grip, either in its metallic-and-wood or plastic version, is a compromising piece. You have to build it in a secure place. Because it doesn’t require special machine tools, it is possible to manufacture it in private homes.

The barrel is the most critical part of the process. For accuracy, a gun must be rifled. As indicated above, it is possible to rifle a barrel with primitive tools, but this is inadequate for a large-scale production. You must therefore find a way to smuggle industrial barrels. I recommend importing finished barrels whose cartridge chambers have already been machined. To smuggle these components, it is wise to use the ant strategy; i.e., import a small number of pieces over and over. It will minimize loss in case of interception and deflect suspicion of a large-scale operation. Barrels can be easily concealed in metallic pipes, imported as bars, or hidden in a truck chassis.

Magazines should also be purchased from industrial sources.

Final assembly should also be done in a secure place. Since the quality of manufacture is difficult to control under clandestine conditions, only after the final assembly will it be possible to test whether the guns work or not. Therefore, you must have a place to fire the guns, without alarming the whole neighborhood, with an adjacent workshop to make the final corrections.

An important element in this production scheme is theTh distribution of jigs and tools to the various manufacturers, especially for the small pieces.

Buying barrels or magazine is not practical, of course, for truly clandestine manufacture in a denied environment. To truly have a clandestine arms factory you must be able to make these difficult parts, and you must also be able to make ammunition.

To keep such a factory in the face of a hostile intelligence or security service requires full-on tradecraft, including isolating links such as cut-outs, and clandestine communications and logistics. It’s a tough set of conditions to meet, especially behind enemy lines. But we can learn a little from the organized criminal enterprises that have done this before, and a little from the resistance organizations that have done this before, and we can apply logic and reason to the problems that might arise.

Testing Polymer Receivers to Destruction: Factory and Printed

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

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

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

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

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

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

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


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

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

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

trouble1 delamination 2


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

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

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

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

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


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

Lost PLA Based 10/22 – From Data to Print to Cast Aluminum

We have mentioned before that the great benefits of 3-D printing include not only the direct printing of parts, but the printing of tooling, models, and patterns. It was inevitable that sooner or later someone was going to 3D print a PLA (polylactic acid, the easiest and most common plastic for 3-D printing) pattern for a firearm receiver, and then make an aluminum alloy casting using the Lost PLA process, essentially identical to the lost wax process used by jewelers and dentists for millennia. And now someone has done it, yielding this receiver, which builds up into a clone of the popular Ruger 10/22.


The 10/22 is a good choice, as a vast quantity of aftermarket parts are available for this rifle, and the original receiver was designed to be produced by investment casting in the first place.

Here is the lower receiver as a 3D .stl model, set up for slicing and printing.

Here is the lower receiver as a 3D .stl model, set up for slicing and printing.

In Lost PLA, the pattern begins as a 3D dimensional file.

Receiver as printed. Note that all pictures in this post can be clicked to embiggen.

Receiver as printed. Note that all pictures in this post can be clicked to embiggen.

The receiver is printed (allowing for a shrinkage percentage), then rods of PLA or wax are attached to form sprues, runners, fillers, and risers (sprues attach multiple parts; runners direct molten metal to parts or to areas of parts; fillers are used to pour the metal in, in most cases there should be only one per sprue; and risers allow air to escape, and signal the completion of the pour).

Investment packed into a flask. one of the tubes leads to a filler and one a riser.

Investment packed into a flask. one of the tubes leads to a filler and one a riser.

Then the assembly is invested with high-temperature plaster or plaster and sand mixture. The wax / plastic pattern is then burned out of the mold, and the metal is heated and poured in to the investment.

The casting with filler and riser still attached.

The casting with filler and riser still attached.

After the pour has had time to solidify, the casting is removed and any risers and screws are cut off.

Another thermoplastic like ABS can be substituted for PLA, but not a thermosetting (for obvious reasons). We expect PLA to be superior on castability.

In this case, the casting looks like it needed some cleanup (here’s a close-up) before it was built into an actual firearm. That’s not uncommon for investment castings, although industrial investment castings get nearer and nearer to net shape all the time.



You want tutorials? We got tutorials.

Here’s an Instructable in which a series of lost-ABS Yoda heads (people want Yoda heads? Takes all kinds to make a world…) are attached to a wax sprue, invested and cast. You could easily see this done with small parts and some other metal (although most home and small foundries aren’t going to be casting iron or steel due to the temps required). There are many practical tips for insuring casting success in this one, and an 11-minute at the end that ties it together (mute the sound). Read the comments too; the guy has decided PLA is better than ABS for this purpose.

Here’s a walk-through of another lost-PLA art project. Note that burnout temperatures are specific to materials and, especially, investments. Follow the instructions of the investment maker.

Here’s the original lost-PLA project we first cited some years ago, but it’s still valid.

And a Hackaday they’re hacking lost-PLA in a pair of Microwave Ovens. Here’s a quick overview with many links, and here’s the actual project. One Microwave is a standard one, and uses a susceptor (think metal, focusing the energy) for burning out the PLA. The other is converted, removing the rotisserie and using a top emitter to melt aluminum. Of course, this is limited in size/volume/weight of part it can do.

We would give them a safety thumbs down on their cardboard-box flask. Cheap, yes, but… and they don’t disclose much about their aluminum melting mod to the microwave.

And finally, in Make’s Ultimate Guide to 3D Printing in 2014, they showed a couple of other ways to make metal parts, some decorative (like low-temp bismuth alloy).



A Sad Gunsmith Story — And How to Avoid One

A guy on Reddit has a pretty sad gunsmith story. In Reddit tradition, in memory of the martyred Chairman Pao, we’ll give you the tl;dr version first:

tl;dr: guy brings three gun parts to shop for smith work. Never meets with or talks to smith. Parts are on budget but are late and low quality. 

OK, here’s the way he put it:

I was referred to Williams Gun Works by a local Wichitan. I wanted to have a factory 10/22 barrel threaded and a Beretta Neos 6″ barrel threaded. I also wanted my Glock 17 slide milled for an RMR and cerakoted to match.
I contacted them and they told me to bring the stripped barrels and slide as well as the RMR. I dropped everything off on June 4th and noted one scratch on the 10/22 barrel so we were on the same page as far as cosmetic defects. They didn’t have the first clue about milling a slide for an RMR or the barrel threading but assured me their machine shop guy would know. They told me it should be done in about 2 weeks give or take.
6 weeks later (7/15) I get the call to pick up my barrels. The slide still wasn’t done though. Still waiting on Cerakote. They told me to bring my can to make sure the threads were good. I decided it would be best to check the threads with a nut first, just in case they were fucked up. I specified the exact length/type of threads I needed for that can, though.
I take off work to go pick up the barrels and I immediately notice a good amount of surface rust on the 10/22 barrel. They rubbed it with an oily cloth and called it good. Threads were ok though.
The Neos barrel had some surface rust that was new as well, but also had really fucked up starting threads and wouldn’t catch a thread at all. This was a surprise to them (implying they had even looked at it before calling me).
They ran a die over the threads and I was able to thread the nut. I took both home and cleaned up the threads further with my own die, and removed all the surface rust.
Today (7/20) I get the call to pick up my slide. I take off work again. They had already mounted the RMR. Cerakote looked good. The extractor plunger wouldn’t go in its hole.

Did you guys see the red flag we did? Let’s rewind:

They didn’t have the first clue about milling a slide for an RMR or the barrel threading but assured me their machine shop guy would know.

So, despite the fact that someone recommended this gun shop, they send their machine work out. (Not unusual). And they don’t even know enough to talk about something that is, frankly, a pretty common request. (That is unusual). How common? Well, Glock made flat, optic slides a factory option because enough people were doing it that it began to make sense in mass production. A slide already set up like that is a phone call away. And the explosive growth in NFA registrations in recent years is predominantly in suppressors, which need threaded hosts — again, something so common that vendors are series- if not mass-producing the barrels and selling them on GunBroker. It should have been a red flag that the shop’s guys couldn’t talk intelligently about these two simple procedures, and didn’t pass him off to someone who could. (Sure, a simple sales clerk might not know, but can’t he say, “Willie’s in Tuesday, and he understands all this stuff. Can you come in to see him?”)

There was another clue that they sent this work out, also:

[T]hey told me to bring the stripped barrels and slide as well as the RMR

Now, having the barrels stripped does make threading easier, but disassembly is a pretty trivial thing on these two firearms. They’re both designed with assembly and maintenance in mind. But the shop’s insistence on stripping suggests it’s going to a shop that doesn’t have an FFL and probably doesn’t do much gun work.

That’s not necessarily a bad thing. Gun work was at the cutting edge of machine shop practice 150 years ago, but today a lot of shops routinely work on ultra-high-precision tools and dies and aerospace parts. They should be able to set up and thread a gun barrel sleepwalking.

But working through a shop that sends their stuff out means you’re trying to communicate what you want done through intermediaries. And in this case, the intermediaries sound unprepared for and unfamiliar with the work in question, even if the shop (from whose knowledge the second-hand nature of this job insulates the customer) isn’t.

In our limited experience gunshop clerks run the gamut from real experts to complete bozos. The best of them know their products and the market, and know everything they’re likely to see as a trade-in, too. They can talk gun history and manufacturing processes with the best of us. The worst of them? Should probably wear a hockey helmet while out in public. But they all think they’re experts, except for the real experts, who are paradoxically more humble than their station should demand. But the particular experts at this store never told the machinist about the importance of corrosion control and deburring (and then, there’s a little voice that tells me if you don’t understand corrosion control or deburring, you’re probably not a real machinist, either).

It sounds like nobody took ownership of the rust on barrels. That’s a double red flag, first that the barrels were allowed to get that way, and secondly that it was received with blasé indifference. It’s like going to a plastic surgeon for a nose job and getting that, and a bonus Teutonic saber-dueling scar.

This guy wound up spending $500 for work that was never QCd adequately by anybody and having three guns down for a month and a half. Work that he needed, in some cases, to do over. The shop did offer to blast and restore the Cerakote on the Glock slide, as removing enough of the burrs to assemble the pistol left bald spots on the slide. The seller chose not to give them a second at-bat with his pistol; he’s still so POd that he’s talking about a credit card chargeback (something merchants really abhor).

Even without having seen their side of the story, it’s a dead certainty that the shop, too, is unhappy with this transaction all around.

The guy could have bought a Glock slide cut for RMR and a threaded 10/22 barrel from almost anywhere, like Brownells, One Source Tactical or Lone Wolf (at least for the Glock part), and had overnight delivery. He’d have spent a little more money; the slide goes for $250-300 finished while the milling job is done by many production smiths for $120-160 plus shipping. We’re not sure about the Neos barrel, that’s a bit of a rara avis at this time, at least compared to Glocks and 10/22s which have an ultra-robust aftermarket.

How do you avoid this predicament?

There are several things  we recommend.

  1. You may not want to use a local shop. There are shops that solicit your business and that do business nationwide.
  2. If you can’t talk to the guy who’s going to cut your metal in a local shop, they send it out to some generic job shop where it gets treated like generic machined tractor parts or whatever.
  3. If the guy says they don’t know how to do something, don’t browbeat him into trying it and then regret it when he fails. Instead, take his word for it. This is not the smith you are looking for.
  4. Don’t pay 100% in advance. In fact, withhold something until the job proves out. Think of those dollars as your hostages to a successful transaction.
  5. What’s the point in dealing locally if you don’t deal face to face with the actual smith? A lot of people today seem terrified of communication by phone or face-to-face with actual humans, but this guy didn’t have that problem, he just communicated with the wrong guys.

From the Dealer’s Point of View

  1. If you send work out, be up front about it. (“Hey, that’s a milling job, we don’t have the machine tools for that, but we do have a good shop that does work for us.”) Nobody will hold it against you, you’re a small business that needs to interface with other small businesses to please your customers.
  2. Don’t let a customer talk you into work that you’re not sure you or your guy can do.
  3. Never, ever, take a job you don’t understand completely.
  4. Never, ever, release a job without inspecting it to ensure it met what you quoted. (What, no quote? See next item).
  5. Quote in writing and in detail. This protects everybody, yeah, even the merchant.
  6. Consider hiring (or teaming with) a real smith if your market will support it. If you’re really small, see if you can get a guy to come in one evening a week (most of your customers work day jobs) or make a weekend presentation on what he can do. It is not the walk-in repair and modification business that will pay for the smith, but the impulse purchases of the guys who come to see him. You can also use him to raise the profile of some of your plain-jane used guns.
  7. Don’t oversell your smith. We watched an alleged smith fail miserably at reassembling a customer’s common-as-dirt Winchester .22. He didn’t have the humility to go to YouTube for an answer, and the old standby of using two screwdrivers to compress a long spring into a short hole didn’t occur to him, probably because he got rattled by several failures. If a guy isn’t a real gunsmith, don’t call him that, call him a technician, armorer or repairman.
  8. If you’re the smith, be humble. There’s no harm in asking if you can look at something, check some references, and then quote.

For everybody, meet the other party half way, and try to be sensitive to their expectations. We actually think the shop in this case did that with their offer to re-coat the slide; we think the customer’s being unreasonable if he wants a full refund. But the shop really blew it by returning uninspected work to a customer. Now the guy has lost faith in you, and, he’s dropped the Reddit bomb on you, which is on the net forever, or until Reddit management finally kills the site, whichever comes first.

Do We Need A Bigger Bullet?

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

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

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

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


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

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

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


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

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

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

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

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

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

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

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

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

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


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


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

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

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

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

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


GunLab’s Reverse Engineering

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

MP44 reverse-engineered trunnions

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

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

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

Say “Thank you,” class:


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

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

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

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

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

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

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

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

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

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

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

Note on an Unpleasant Subject

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

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

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

It’s About Time: Army Looking at JHP Ammo

9mm_124grain_jhpThis week industry contenders met with Army evaluators in the final Industry Day for the XM17 Modular Handgun Program, and the most interesting news is that the JAGs are finally on board with using jacketed hollow point ammunition in the new pistol.

This has several consequences, assuming that these lawyers are overruled by other lawyers somewhere down the line:

  1. It increases the defensive utility of the firearm against unarmored enemies, although not nearly to the level of a rifle or rifle-caliber carbine.
  2. It just about guarantees that, modular or not, our next service pistol will be firing the 9mm. The 9mm is as effective — with modern JHPs — and much easier to shoot than .40 S&W or .45 ACP, and it offers greater magazine capacity. (See Loose Rounds’ repop of the FBI report that justified the Bureau’s return to 9mm from .40).
  3. It means that most of the “modular” advantages the XM17 proposal wants are kind of pointless. The Army wants a service pistol and a max-commonality concealment/compact pistol. Since users seldom go from requiring one to requiring the other and back — the set of concealment/compact pistol users is small, as M11 procurement numbers show — the whole “modular” theme of the procurement is a bagatelle.

Bob says these are the criteria, apart from improved ergonomics relative to current service pistols.

  • non-caliber specific
  • modular grips
  • grip that accepts a wide-range of hand-sizes (5th to 95th percentile)
  • ability to accept different fire-control devices/action types
  • ability to accept various magazine sizes
  • suppressor compatible
  • ability to mount “target enablers” (lights, lasers, etc) on a picatinny rail
  • match-grade accuracy (90% or better chance 4″ circle at 50 meters)
  • low felt recoil impulse

Not all of these are widely useful (explain to us why a military unit will need their pistols “to accept different fire-control devices/action types”?) but some clearly are. The ones that are most clearly useful, of course, are widespread in modern handguns.

As far as the pistols go, according to Owens, the interesting contenders are the STI/Detonics, the SIG P320, and the Beretta APX. We find it hard to believe that the 1911-based STI/D is seriously in the game, or that the brand-new APX is sufficiently developed. The 320 (with a safety) does seem to meet all the requirements. Unlike Owens, we’re not ready to write Glock and S&W off, and would be very surprised if both of them didn’t  make serious and credible proposals.

Here’s Bob’s story on the JHP reveal at the briefing, and here’s his story on what he considers the leaders of the modular handgun competition. Note that there is one small error or oversight in his JHP story, and that’s his statement that US SOF have used 9mm and .45 JHPs. To that, we’d add .40s. (Certain specific units use this caliber). The Gun Zone’s Dean Speir wrote a post years ago on the legalities as observed by SOF since 1985.

Don’t Get Too Excited

Given the marginal role handguns play in combat, the adequate supply of current M9 and M11 service pistols (as well as non-standard pistols in some units), and given the rampant downsizing of the Army (it has less than half the combat power it did in Cold War days, and is scheduled to lose another 40,000 men, mostly “tooth” not “tail”), this entire program is a waste of time and money. If the contract goes forward, the Army will buy about a half-million service pistols plus some tens of thousands of compact variants for all services. The Air Force and Navy are accustomed to having the Army do their small-arms purchasing. The Army plans to force-feed the new modular pistol to the Marines, who are explicit about their lack of interest in it.

We’d be very surprised if this proposed procurement came to pass. If the Army doesn’t kill it, Congress will.

But the final approval of JHP ammunition for non-SOF pistol users is long overdue. In fact, it’s the single biggest thing they can do to improve the utility of current service pistols, and it can be done without out tests and contract disputes (hollow-points are already in the supply system for DOD police).


Soldier Systems Daily has the PEO Soldier press release with direct quotes from Richard Jackson, Special Assistant to the U.S. Army Judge Advocate General for Law of War.

Debi Dawson, PEO Soldier spokeswoman, also noted that by “modular” the Army means “allows adjustments to fit all hand sizes.”