What type of semi-auto action in a 3d printed rifle

S

superking75

Inactive
Ok before I start yes this is an off question and I don't think I will ever try it but, I would like to know.

If you were to make a semi-automatic rifle almost completely by a plastic 3d printer(Of course somethings just can't be:barrel,chamber,firing pin etc) What type of action would it have and how would it work? Why?

Or any just outright idea on 3d printed firearms.
 
Add action (assuming you mean receiver by that term) to that list of metal objects.

I'm not aware of any plastic that will have the hardness and strength- and probably abrasion resistance as well, required for the pressures and bolt thrust generated by centerfire cartridges; but I'm no engineer and have little knowledge of "exotic" plastics.

Maybe a .22 rimfire, but that's a different animal.
 
I would use a simple blow-back action chambering the lowest pressure cartridge I could find.

You'd need a good-sized 3D printer since the bolt would probably be the size of a car.
 
"...some things would need to be metal..." Think in terms of everything that's steel now CANNOT be plastic. Any cf rifle works at over 45,000 psi of pressure. AND the plastic would have to be 100% fire proof.
 
The least amount of parts that can be metal, in my eyes, include the bolt carrier group, barrel, locking lugs, and barrel extension/trunnion. Considering the complicated machining of these parts, it would kind of defeat the point of 3d printing. What thought experiment are you pursuing?
 
The only gun design that would even come close to working, with a plastic receiver, would be the inertia driven system similar to Beneli's shotguns, where you would still have a steel rotating bolt locked into the rear of a steel barrel. Then, many parts in the trigger group, and most likely the feeding group, would have to be steel, as they can't be allowed to flex.

The problem is the plastic, and I would say that it would have to be a reinforced fiber plastic (glass fiber reinforced polymer), which is molded, to keep the barrel's recoil from cracking the plastic receiver. I'm pretty sure you can't get plastic of that sort for a 3D printer, as the fiber is mixed with plastic when it is molded. The only other way, would be using an extra-thick receiver of something like Nylon.

Another problem is the wear of the bolt in the ways, if they are plastic, and how soon that would wear out. Well made plastic pistol frames are molded around a steel frame insert, with steel ways for the steel slide to operate on.

You can do this in low powered rimfire cartridges, in .22 long rifle, as that has been done by Remington, (Nylon 66), however a steel bolt and barrel was used, along with steel trigger group parts, and a sheet metal receiver cover. The one model that they tried with plastic trigger parts was a complete flop.

Even a .22's bolt has to have so much mass for it to work correctly, and there would be no way of getting that mass, unless it was a big chunk of plastic weighing the same, that could take the pounding.
 
It might be a rifle, but that doesn't mean it has to be a rifle cartridge.

I'd stick to lower pressure CF pistol rounds. Would .45ACP qualify?
 
CF pistol ? You have two problems ,pressure , and bolt thrust .
With a 22rf both bolt thrust and pressure are low .
With 45acp pressure and especially bolt thrust are much higher.I'm not sure that would work.
 
The only barrel, that I've ever seen, similar was on the Winchester model 59, and that was a composite of a thin steel barrel liner, with a wound glass outside. The epoxy merely bonded the glass filament together over the steel liner. I doubt anything such as carbon fiber would hold the extreme pressures of most handgun cartridges, over 1-2 rounds, if made with similar dimensions to a steel barrel. I'm sure that a CF barrel and chamber, that was made thick enough would hold the pressure, but what the bullet and hot gas would do is another thing. You would be back to using Winchesters idea with the 59.
 
^^
Agreed. 100% CF wouldn't work (not a "plastic", anyway), or I'm sure the companies like Christensen and Proof Research that manufacture CF wrapped barrels would go that route.

Totally ignorant on this- so maybe a materials engineer (unfortunately, my son doesn't take that class until next semester :() can chime in. I doubt it's "strength" per se, as CF is many times "stronger" than steel, but more likely is abrasion resistance or physical property of like kind- which would account for why the barrel liner/rifling are still made of steel in CF barrels- and not just the chamber/tenon area.
 
Somebody had a plastic AR whose 3D plot files were downloadable for free for a time, but which the government got upset enough about to announce they were tracking where every download went and to convince the creators to pull the files. But anyone seriously interested would have had them already, and if they were really serious, would know how to make their own.

IIRC, these guys were able to use plastic strong enough to stand up to two or three shots of commercial 223 ammo before the gun broke. Of course the elastic expansion of the plastic would have been huge and lowered the actual pressures very substantially. I doubt the muzzle velocity was very high, but the news story claimed they got enough velocity to be lethal. Smooth bore, close range-only of course. Rifling won't readily engrave something harder than itself. More like, it will be flattened by something harder than itself.

A plastic gun reliable for more than one or two shots of conventional commercial ammo seems unlikely to be readily made with current 3D printable plastics. That said, I understand police in LA have confiscated a number of AR's the didn't have and never did have serial numbers. I'm guessing someone with after-hours access to a CNC machine shop was responsible.

There are metal 3D printers now, too, though I don't know anything about the strength of the finished products made from them, and they aren't cheap. I and most engineers can, I expect, think of a dozen other methodologies to workaround having no commercial manufacturers to make guns for you. I remember in the late 80's seeing a newspaper article on a man in the backwoods of the Philippines turning out a revolver a week from scrap metal in a shop with no electric power. He had one of the old fashioned pedal powered lathes and drills and files and probably some spring stock. That requires skill less common than skilled computers are, but every time someone tells me they think banning guns will end all access to them, I feel obliged to remind them that most have basic mechanisms over a hundred years old, and that while modern tools make them easier to fabricate, anyone with files and a drill and some scrap metal can make one that fires. After that, technology just makes it faster and easier and more precise.
 
In carbon fiber, the fiber itself is extremely strong, but the binding agent isn't, which is still a polymer, thus when hot gas and a lead or jacketed bullet raced down the bore, it couldn't last long, as Unclenick mentions. One would still need a steel liner, and for any accuracy, you would need it rifled. Really, it would be cheaper to just make or buy a rifled steel barrel.

If I were to contemplate a design in this area, I would still use a steel barrel and bolt, and probably make a polymer receiver with a steel insert, to receive the barrel, and provide raceways for the bolt to travel in. I would look at a glass reinforced polymer for the receiver itself, along with the trigger guard, which would house a steel hammer, sear with disconnector, trigger, and safety, all mounted on steel pins.

The hammers sear and disconnector notches, the sear, and the disconnector hook all need to be of steel, and hardened at that. If not, they would wear out quick, but not as quick as a polymer. Plus, as Unclenick mentions, the dimensions would change more, due to a higher expansion rate.

I did see a video of them using crude tools, in the middle-east, to turn out weapons, and they did it rather well. Some of those shops are used to doing things the old way, similar to our early gunsmithing and blacksmithing shops of yesterday.

One last thought is, that the lighter you make a rifle, the more the recoil you feel, and the more it will kick the bejesus out of you.
 
^^^^
Dixie Gunsmith has some excellent input.

I'll add one thing as a former design engineer. As you change materials, the way you design an item generally changes, which results in a different look / feel / weight, etc. Trying to duplicate, say an AK or AR with a 3D printer will likely result in a 1 shot wonder or a bomb.

Please don't, unless you have the ability to numerically model the weapon and ensure it's not going to explode.
 
If the goal is simply to make a firearm in an untraceable manner or without access to firearms, there are much easier and more successful ways. Look at the Luty SMG and the Sten, for starters. Single shots of any kind are very easy (basically just a breech block and a barrel). Open bolt submachine guns have been turning up in South America, Australia, the Netherlands, etc. appearing to be made in factories somewhere. One could be made easily with some pipes, steel round stock, a lathe and a welder. A drill press and some files could likely substitute for the lathe and safety of the operation is simply assured by the weight of the blowback mechanism. That's all theoretical though.

The only utility I see for 3D printing now or in the near future is replacing hard to find parts that are not structurally critical. I've already seen vz. 61 skorpion lower receivers 3D printed. Stocks and other furniture is a possibility also I guess. 3D printing is relatively inaccurate and creates a much more porous (weaker) material versus even traditional plastic machining.

The 3D printed metal (sintering) may advance, but I don't see it replacing forging and machining. I see it replacing casting as a rapid and cheap way to shape metal (less finish machining required probably) but I don't know if it will ever have the strength of properly forged steel. Just my guess.
 
Guys in my state are buying 80% lowers and finishing them out with a router for a great AR. Then building the rest from parts as they like. Perfectly legal.
Seems to me that building a ghost gun should be easier than 3D printing the printable parts for one. But it would be pretty cool if you could 3D print most of your other parts for a ghost gun project just for the heck of it. Sounds like a lot of fun.
 
Things may change in the future, but the only thing I can see coming as a result of claims about "printing out a rifle" or "making a thousand AK-47's at home" is to help the anti's extend government control over private computers. If government control can be extended over computers and peripherals on the grounds that they can be used to make "untraceable" guns, the left will cheer computer licensing and applaud police raids on private homes to "fully implement gun control". Count on it.

Jim
 
If I were to design something, what would I do?

1. The bolt carrier locks into the barrel (AR-style) rather than into the receiver (FAL).
2. Use a simple U-bent sheet of metal to locate the pins and resist their tendency to elongate holes through pounding (Think of the trigger group that rests inside a G3/HK91/93 receiver.
3. Use a simple BCG recoil control system, such as the single piece of metal that guides the bolt on a Bushmaster M17

Heck, for that matter I'd probably just make an M17, the lower was polymer and the upper was a simple quadrangular tube with a few pivot points that could be replaced with nuts n bolts for simplicity.
 
Jim, you're spot on about that.

I was watching a video the other day, and now they have some monster 3D printers, making concrete houses in China, and I think a guy patented one here in the US for that. How well they'll hold up, if the ground gives a hard shimmy, is unknown yet, as there's not a drop of rebar in them. They'll probably last about like a concrete block structure.
 
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