I’m interested in helping research towards making higher-caliber weapons possible with fully DIY components. I’m still not that well versed in weapon design and I know many people here have more experience with converting components so the main thing I’d like to know is what limitations need to be overcome?
I have an idea for the ECM taper that may work but it’s yet to be tested. The other complexity is the bolt carrier group and the locking mechanism but I think that can be made with guides. The other consideration is the gas system, a section could be attached to the gas port without welding with a clamp but then I’m not sure if direct impingement or a piston system is the way to go.
Any help is appreciated.
Just my $0.02, but I don’t think polymer FDM technology will ever be suitable for gas system components. So if you go down that path, you’re looking at sophisticated DIY metal parts that it will put the design out of reach of most people. ECM may be viable for some of these parts, but there’s a pretty big skill gap between cutting a barrel tube to length (where actual length doesn’t matter at all to the process), and cutting bar stock to the rough sizes and shapes needed to fit ECM jigs. Take a look at the Rogue/Rebel 9mm bolt instructions for an example of a steel assembly that’s pretty close to the limit of DIY-ability.
IMHO, the key to handling more powerful cartridges is figuring out how to do a delayed blowback system that is easy to DIY. I’d suggest doing some research into lever-delayed systems (Forgotten Weapons has a good intro here: https://youtu.be/utv6LK6CxJI ) and thinking about how existing DIY bolt designs might be adapted to utilize that. I don’t know if it’s practical to get all the way to full-power rifle cartridges with a lever-delay system, but it definitely has potential for intermediate cartridges like 5.56x45 or 7.62x39.
I think expectations need to be maintained when making higher caliber weapons. I think what would count as “DIY’able” to me is for the gun to be made in Europe with no special equipment or custom parts, only with FDM, standard tools and common metal parts (except the barrel). Without welding is ideal but not necessarily a requirement.
Delayed blowback does not really solve the problem because it wouldn’t work for stronger rounds (or it would likely be unsafe). For a piston system (for example) a steel block could be used, then one hole drilled that connects to the gas port hole and then one larger drilled hole containing the hammer system. The hammer used could be a common metal part that simply fits the diameter of the drilled section.
It would help if you define what you mean by “higher caliber”. The French AA-52 was a lever delayed 7.62x51 and the Soviet Garanin was a lever delayed 7.62x54R. The French MAC-58 was a lever delayed 50 BMG! And of course the H&K G3 in 7.62x51 was a roller-delayed blowback system.
If you do the math you’ll see delayed blowback is every bit as viable as gas systems for pretty much any caliber. Gas systems are more prevalent now simply because they’re cheaper to produce, have higher tolerance for harsh environments, and tend to have longer service life, but neither of those are really priorities for privately manufactured firearms for civilian use.
It does seem like an interesting route. Only thing is that it seems like it would put a lot more force on the receiver from the accelerator lever so a metal element would probably have to be inserted in the section of contact. I think my concern with that is that it would put a lot of stress on a polymer receiver, yes there are examples of higher caliber weapons in production with a blowback system but if the receiver is less strong then it could put too much stress on weaker components and it could be a safety concern. I’m still learning but this is my view right now.
By higher caliber I mean higher than current hybrids (9mm) so 5.56/300blk and 7.62x51.
The big problem is mostly being able to manufacture locking geometry. ECM can do rifling, but it can’t do – say – the barrel extension on an AR barrel. Cycling is whatever, we can figure that out, but we can’t fire 5.56x45mm unless we can keep that breech closed.
There was one guy who did a flywheel-delayed blowback rifle a while back, but he ended up dropping the project. He tried to do a rack-and-pinion setup with the rack on the bolt and it would just violently shred the teeth after cycling. Personally, I think there’s still potential there, but there are probably also much more novel approaches we haven’t explored yet.
I think a blowback can’t really be done at higher calibers without too much internal stress for these calibers. I think right now making a DIY gas system isn’t the priority, first is making a working bolt-action higher-caliber as it would still require a lot of development.
Just boils down to figuring out locking geometry, yeah
Trying to think of a simpler mechanism than rotating bolt lugs. The lugs on a typical assembly could be made from a steel part with a rim on one side and filed down using a guide and then drilled through the middle for the firing pin. The main issue I think is the complexity of the bolt internals. It may be possible to FDM some of the internals that don’t take the brunt of the stress (maybe in a CF polymer) though again it may just explode.
If not using direct impingement the bolt can be simpler however it would still take many drill guides. The extractor and the breech face lock itself seem difficult to make unless they are changed.
I suppose if a barrel with taper could be successfully made with ECM then the breech face could be as well with the same principles? Maybe with 6 wires just inserted into the end so that it creates the pieces to lock into. I definitely need to do lots of experimentation so see if all of these ideas are possible.
I would suspect the right way to work our way towards a fully DIY intermediate caliber design is to handle one part at a time. So start with a design that only DIYs the barrel, or the bolt, etc., then progressively step towards turning more parts from commercial to DIY.
I’d be curious to hear more about your ECM taper idea. What can you share about that?
I think making the DIY barrel should be the first priority. For the chamber a usual method of ECM can’t be used so my idea is to use a linear motor that travels along the taper with precise timing to remove more material at the start and less at the end to create a smooth ramp. This paired with a copper ring that would selectively reduce one small section at a time. A lot of these DIY processes for ECM seem to have too many variables for failure, in my opinion it is more ideal to have a standardized system for ECM to prevent outside variables impeding accuracy. This can be done by printing everything (even the container) and making the motor/ECM process itself controlled with a microcontroller.
Just to note I’m not sure if this idea for ECM is even physically possible as I’m not experienced with it.
I recall that Jeffrod was working on a more precise method of ECM that may be similar to what you’re describing. No idea where that ever landed.
There’s a question I feel that should be asked more - why aren’t chamber reamers used more widely as part of the “DIY barrel” process? Are these reamers unobtainable outside of the US? I recall looking at that a while ago and it did appear they could be shipped worldwide.
Seems like a high-risk item to purchase, higher-risk than any other bought component.
An update - I’ve created early designs with full theoretical functionality, including a short stroke system and a locking system. I need to refine many aspects and then fdm test parts as placeholders for the metal to stress the mechanical elements function.
