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Just wanted some input on my latest idea. For a while now, I've wanted to make a smaller bore cannon for those pieces of spud left over from my larger 2 inch and hybrid cannons. I also really like the idea of cartridge fed gun, by which I mean stuffing small pieces of pipe with potato to make 'bullets'.
Any way, I got myself a 1/2" QEV and a 3-way DCV to act as trigger, and began planning how I was going to put it together.
My priorities for this build are aesthetics, and for it to actually function like an automatic mag fed firearm. Power is NOT a priority, since I have my hybrid for that I've already done some test shots with a small piece of 1/2" pipe for a chamber on the QEV, and an equal size pipe for barrel and it is plenty powerful enough for my needs at 125 psi. I am planning on doing a simple blow-forward bolt in the 1-inch pipe section, and hopefully figure out a way to incorporate a method for cartridge ejection.
As follows is a mock up of how I plan to put it together. I started with an AR-15, and positioned the chamber of the QEV as a mock scope, where one end is actually a pressure gauge. As some may know, I have a 3D printer and will be making the body of the gun outlined in red with plastic. I will also be able to make my magazine(s) from plastic as well:
Obviously these are very rough. I just wanted to get them up tonight so you guys could look them over. I will be doing more detailed modelling of the guns body later on and will get that up as well.
Mainly wanted to see if there was a potential problem with the set up. I am a bit worried about the air flow in the 1/4" line coming from the trigger to fill the valve, it should only slow the rate of fire, correct? I couldn't figure out another way to drop the trigger down to where it should be.
Let me know what you guys think.
The blow forward bolt catridge ejector(where the mag will be) is away from the trigger ,in most of the assault rifle the magazine is close to the trigger eg: M4,M16A2,AK-47 and for rest it mostly bullpup configuration like Famas and Steyr AUG. In your drawings above, the AR-15's mag is close and your guns mag is away from the trigger.
If your main priority is aesthetics then I suggest you change the body from AR to HK-G3SG1 sniper rifle which has the the mag away from trigger maybe you can place the mag a bit further and not mess up the actual look of the gun.
Also another assualt rifle which my country uses is Type 81 (below), has mag far from trigger ,
just some ideas to make the look more realistic.
I completely agree with you. Having the magazine well closer to the trigger is something that I hope to achieve. Unfortunately, I think it would require moving the QEV back further to make room for the bolt. In that configuration, I don't know what I would do with the chamber, as a scope would look funny back that far.
I used the AR-15 for a reference to get the grip and trigger in the right spot with respect to the barrel and action. I haven't designed the bolt and ejector yet, so I likely exaggerated the length of that section, so by the time I'm done I hope to reduce the length of the 'reciever' part of the gun.
Have a look at my own cartridge ejecting endeavours, you can simplify the design considerably:
Would shop air pressure be enough to actuate such a blow-back design? I think I can compact a blow-forward design quite a bit, by pushing the cartridge forward with the bolt like you have done, and bringing it back to the ejection port. Do you think I am better off with a blow forward or blow back design? I'm not sure how I would route the air from the QEV to in front of the bolt in the blow back case...
My very first effort was sort of working at 115 psi:
With a high flow valve you should be fine.
Your idea makes a lot of sense, but it entails building cartridges with a rim, a bolt with a claw to pull the cartridges back, and a ratchet-like extractor that allows the bolt and cartridge to go forward but ejects the cartridge when the bolt goes back. If you can do that, the result would be awesome
One comment about your pop-off design, I would feed into the firing chamber, not the pilot area in order to improve efficiency:
I was thinking a bolt that is the same OD as the ID as the cartridge, with a tapered end and depend on friction, and perhaps an o-ring to pull the cartridge, rather than a rim and outer claw. As for the extractor, I was going to put it slightly behind where the cartridges come into the breech, and just have the bolt move back far enough to make use of it. The smaller diamater of the bolt wouldn't touch it, but the cartridge would flip out. Just a smaller machine screw through the side of the breech pipe would suffice, wouldn't it?
As for the QEV, I have one of the pilot-filling variety. Are you suggesting fill through the chamber on the A port, and just have the pop off valve on the P port? I had a look at the internals and I don't think that will work, air would just go right out the R port. It's pretty much a miniature barrel-sealing piston valve.
Re: .50 Galv Steel Full Auto Catridge Fed Carbine
Sounds like it would work, and provide a decent seal too
Yep, you might want to cover it with some silicone tubing to avoid damaging the shells though.
You would need to modify the piston, in the case of the experiment I had done in the video posted above, I replaced the cup-type rubber diaphragm of the QED with a tight fitting but not airtight delrin disk.
I've been shopping around for pipe to use as a cartridge that would closely match the ID of the 1/2" galvanized pipe I want to use for a barrel. The closest I could find was 3/4", which was very slightly bigger than the ID of the steel, while 1/2" copper tube is very very slightly less than the ID of the steel. Do you think I would be better off with my projectile being slightly larger than the barrel, or slightly smaller? I'm planning on using potatoes, so they'd squish a bit.
As for the QEV, I simply took out the spring and left the cup-style piston in there, and it worked feeding pressure from the chamber side and having only the pop off on the pilot side. Initially I tried flipping the cup shape over so that the air could get by the edges to the pilot side in the opposite direction as intended by the manufacturer and using a spring to keep it closed, but it only vented the pilot and didn't fire the valve. Then, I took out all the springs altogether and put the cup back the way it came from factory and it worked! I guess what must be happening is that there is enough air left in the pilot side after the pop off reseals to act as an air spring and close the valve once the chamber has dumped. With the cup flipped the opposite way, the shape of the cup was such that the air pressure in the chamber pushing on the surface area of the piston wasn't enough to overcome the lowered pressure on the pilot side (which had more surface area). It dumps almost the whole chamber, there is just slight air pressure left after each cycle. However, I suspect that it might be prone to jamming open due to a lack of physical spring if the conditions arise. More experiments are needed.
Check out Amazon for close fitting tubing. They have brass tubing, aluminum, stainless, that all could be used. Hope this helps.
I cobbled together a marsh mellow gun with the QEV to test the automatic functionality this weekend. The pressure source I was using was only 120 psi, so the pop off required a slight pull to get it to shoot. It worked quite well filling it from the chamber side. I had to restrict flow into the chamber with a ball valve to keep the QEV from honking:
https://www.dropbox.com/s/ohexfe2eu1hsm ... 200224.mp4
The thing is freaking loud. Louder than a .22 for sure. It was putting marshmellows through the heavy ply cardboard.
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