3D printing Model Guns/Parts/Cartridges etc

Hi everyone, not really been involved much on the forum recently but with all the lockdown business occurring I figured why not spend my time doing Model Gun related activities! I've had a 3D printer since Christmas and naturally, model guns have been something I really want to explore with the intention of 3D printing my own.

So, initially thought about trying to 3D print cartridges for my existing models, only issue is PLA filament is super weak and one of the tests I did with a 3D printed cartridge with a 7mm cap inside, placed on a metal rod and then hit with a hammer, resulted in the cartridge splitting into several pieces. However, recently, I procured some PETG filament. I was curious because some sources claim it's just as strong as ABS. So, I printed out a cartridge in PETG and did the same test. 4 caps in and the cartridge is still holding together!

So, my plan is to now 3D model and print some model gun cartridges and see what sort of performance I can get out of them. I mean, if AR-15 lowers can be printed on 3D printers (granted, the lower doesn't take nearly as much stress as the upper, chamber, barrel etc) then why not model guns?

So, I think 3D printing such small threads is out of the question so I've been looking at the possibility of other cartridges. The options are...

Open Cartridge: Like the older model guns used such as original MGC M16 and the Mac-11 and even more recent ones like the GM-7 series.

This one: I have no idea what this one is called but I found it on YouTube a while back https://www.youtube.com/watch?v=62IWDSIaKcY&t=199s
it looks like an open cartridge but the cap is forced into the tip and held in place by the star like opening.

Tanaka: And probably the one that I am most likely going to attempt..

So, I'm thinking. 3D print the two plastic halves and then use an aluminium or brass collar to hold the two together, with the cap, primer and plug inside. No threads, quick to make and hopefully strong enough to contain a bit of pressure thanks to the metal collar.

I'm also interested in 3D printing some gas blowback models too but will probably make use of metal components for reinforcement. How is everyone coping with their restricted freedom?

Hi, sounds very interesting and i hope you succeed. open rounds may be the way to go as CP rounds (with a piston) are pretty powerful, if you do get these to work many on this forum will be interested. I cannot give you any advice on this unfortunatly as i know nothing about 3d printing bit keep experimenting, i do know some parts have been 3D printing with a small amount of success in that they work but dont last long.
The video shows a marui combat commander pistol using the marui open rounds,never figured out why the star shape on the rounds, the powder he puts in i believe is flash powder.

Hi Claymore, thanks for your reply and more info regarding the Marui cartridge. As a guess, I would have thought the star shape kept the cap in the cartridge so it doesn't end up blocking the chamber after detonation. I'm guessing the shape of the star will allow gas to vent once the cap reaches the end. That also explains why in the video he has to use a special loading device to seat the cap correctly because I can imagine that would be quite tricky to do by hand without any sort of guide.

The “lands” of the “star shaped” opening of the carts is exactly the same diameter as the bore itself. The purpose of these grooves is solely as a bypass for powder gases / pressure generated by the cap.
The cap generally only stays in the cart due to friction. But if you look closely in the slow-motion sections of the video, you see something small expelled from the ejection port diagonally in the direction of the muzzle. My guess: the cap.

I have a marui P38 and it fired fairly well, but getting the caps out was a bloody nightmare. marui had there own caps and the plastic or rubber they used was more flexible and once fired they were fairly compressed on the bottom of the round. To get them out you have to put a sharp implement into the top and try to prise them out, i still have rounds that i cannot get the cap out of which is a pain.
i never got round to trying them with a marushin or MGC cap, that is something i will need to look at as maybe those caps dont stick in as bad.

I'll be interested in your results

I was never happy with the strength of the parts my FDM printer made.

Ahh, thanks for the info both of you, that's really shed some light now. I'm doing at lot of research into these Marui cartridges because that'll probably be my next attempt.

Okay, so I've got an old GM Colt Government model that uses CP cartridges by default but it doesn't blowback the same anymore (I think the pistons have mushroomed and they're not completing their full stroke inside the cartridge. I figured 45 cal cartridges would be better as they would allow for printing with thicker walls which is important for pressure. I studied the GM-7 open cartridges and 3D modelled one ready for printing. I also made a new steel detonator with groove for an o-ring.

I used the brass "primer" from the CP cartridges I have and loaded up for testing. The caps all went off first time but no blowback so looking at the detonator I noticed the o-ring kept separating from its groove so pressure wasn't building. I kept reloading and firing the same cartridge by the way. So, I then made a new detonator pin with more material to keep the o-ring in place and this time when I fired, the cartridge split into 3 pieces. I figured the material had weakened after each previous shot but at least now pressure was building up.

I'm printing another open cartridge and this time I am going to coat the inside and outside with super glue for strength and for a smoother surface to reduce friction. I'm also going to use a slightly weaker recoil spring to give it more chance but of course it's going to be tricky to balance the strength of the recoil spring since open cartridges have more resistance during feeding.

If this doesn't work, I'm going to try out designing a Marui style cartridge with the cap facing the other way and see how that goes. Not giving up just yet.

Sorry 8ace, didn't see your message. Thanks, I'll keep you all updated and hopefully get some pics or a video if I get any decent results. What material were you printing with? I'm using PETG currently but it's a shame that my printer can't use nylon without hacking the firmware.

SUCCESS!!
I just altered my design so it featured the Marui style cartridge star and also widened the "primer pocket" so it could use the Marushin style primer (the one with the O-ring) since this design has the cap facing towards the back so need to keep the gases from escaping.

It didn't go off straight away because the primer hole was a bit too tight but on the third hammer strike it made me jump out of my skin because suddenly, pop, loads of sparks and recoil and the cartridge went flying.

I still need to tweak the design however. The cap didn't stay in the cartridge but wrapped itself round the detonator in the chamber. I need to bring the star pattern in the cartridge ever so slightly tighter and the detonator needs to have a flatter tip to stop it punching a hole in the cartridge.

Update
Okay, so I've now ran out of caps after so many tests but I think I have pretty much finalised my design. The biggest issue I had was the cartridges splitting after 5 shots. I mean, if you think of these as disposable then that's not an issue but I decided to alter my design to include a 12mm aluminium outer collar for added strength but I'm still keeping the Marui style design for simplicity sake.
However, I can't yet attain full blowback on a single cap. My only successful test was the one where the cap was "allowed" to exit the mouth of the cartridge and impale itself on the detonator pin. I have a feeling with my new design where the cap is retained by the cartridge the cap (acting as a piston) doesn't travel enough to generate enough inertia for a full stroke. This must be why the gun stopped cycling with its original CP cartridges. The deformed pistons aren't completing a full stroke so the slide doesn't have enough force imparted upon it.
On the 1911, the slide needs to travel about 2 inches so I need to either accommodate for more "travel" in the cartridge by reducing the length of the primer or, use a 7mm+5mm cap which is standard practise for the Marushin M16 series.
Or, I could always attempt making my own model gun like a Mac-10 and see if that can cycle with these custom cartridges. I'm going to keep trying though.

have you thought of looking at the tanio koba open round system which uses a det pin with a rubber seal on it, it may give you the pressure you need for blowback, could also be too powerful and blow the round as tanio open rounds seem to made of a resin type material.

Hi Claymore, yeah that was my first attempt and 3D printed design. I printed an open cartridge using the MGC Primer insert in the base and a custom detonator pin with an o-ring. The pressure with this setup however always caused the cartridge to blow up. I have a feeling the Tanio Koba cartridges are made from Nylon which is a super strong plastic (right now I'm only using PETG filament for printing which is pretty strong but not strong enough). My 3D printer could potentially print Nylon but it means hacking the firmware for higher melting temperatures.

My only logical explanation is the balance of recoil spring resistance, hammer spring resistance, friction in the cartridge, power and cap/piston travel. To be perfectly fair, the open cartridge design could be revisited if I use 5mm caps as that would allow slightly thicker walls during 3D printing. Still got a lot of experimenting to do though, once I buy some more caps.

There are not that many options for the cartridges - they could ideally be cheap single-use ones that shouldn't cost much more than a cap today (a dream), duplicates of the originals (work and material intensive as it requires processing of the metal) or trying to come up with novel ways - as you do!

Even if these initial attempts fail, they provide knowledge and experience to move forward. I suspect that currently plastic (available as affordable filament options) is still too weak to replace metal, especially due to multi-part nature of most cartridges (especially lack of strength in the threaded parts that you try to resolve).
Tanio Koba must know very well what he was doing going for the simple design-wise and material-wise cartridge for his models.

Keeping fingers crossed for your efforts, I'm truly in awe with guys that experiment with the real matter!

BTW - is there any pattern to the splitting, suggesting a weaker point or a weaker plane (longitude or circumference) due to manufacturing process?

For info this is the marui P38 det pin, well its not really a det pin its more of a hammer. you can see the shape of it is different than other other det pins and that is because the marui works slightly different than other models.
The cap goes in with the powder facing inside the round as there is a small pin at the bottom of the round the det pin/hammer then pushes the cap down on to the pin and the cap is its own seal. Now this is similar to the marushin way of doing things but marushins system is way better, one problem with the marui system is the caps get stuck in the bottom of the case and are a real pain to get out and many times near impossible if not impossible without hrs of prodding scrapping and swearing.

Really cool to see and read that there are forum members and modelgun fans that think in an innovative way to come up with solutions for all things related this wonderfull hobby.
It would be great if one would be able to design single use cartridges for modelguns. Ones that could be mass produced for say 30 cent each and easily fit a 7mm cap and would eject after use.
It would make the modelguns even more gunlike and the eternal search for hard to find reusables less of a burden.
Even of comes to 3d printing spare shells, I think cnc would be the best option, above filament.
Keep up the good work boys!!!