Well, I'm in the process of designing the last component to a semi-auto combustion rifle. The very part that would make it semi-auto, the reload system. My first thought was to use recoil to move the piston back but then the issue of not having enough power to produce enough recoil came up. So now I'm playing around with the concept of gas operated "blowback" if you will. Basically it will work something like this:
Basically, for all of you that don't know. It works by using the gases that are built up behind the bullet to push back a piston that is connected to the bolt. It does this to be able to chamber another round. The only problems, that I see with this design is that I would have to get the "timing" absolutely correct. In other words, the piston would only be able to move all the way back to a certain point right when the projectile leaves the barrel. It would have to do that because if it didn't, the cycling of the bolt would break the seal inside the barrel which would cause all the gas to leak out the back of the barrel which would cause the projectile to stop moving halfway down the barrel. Basically the purpose of this was to see if anyone had any advice on how practical this would be. And maybe to come up with alternative ways to cycle the bolt after each shot. Thanks.
That won't work for what he is trying to do... He wants a gas ram to push back the breech, load a new round, and have a spring push it closed again. Like a powder burner.
Bowman, it is possibly, I've seen it done on pneumatic's before, and plenty of others. Getting timing right for refueling a combustion would be difficult though, because you would have to wait for the chamber to vent.
That won't work for what he is trying to do... He wants a gas ram to push back the breech, load a new round, and have a spring push it closed again. Like a powder burner.
Bowman, it is possibly, I've seen it done on pneumatic's before, and plenty of others. Getting timing right for refueling a combustion would be difficult though, because you would have to wait for the chamber to vent.
Right that's exactly what I'm trying to do. Maybe this will help understand?
At first, the design had a combustion chamber connecting to a piston. The combustion chamber was self fueling and self venting. It proved to be a rather bulky design so I turned to the cartridges you see in that link (don't worry I have a ejecting system already designed). So does anyone have any ideas.
Posted: Sat May 12, 2012 3:10 pm
by Goats spudz
the fx revolution uses a system like that, the wasted gas pushes back a piston that recocks the system like an ak47
Posted: Sat May 12, 2012 4:00 pm
by warhead052
Yeah, I know what you are talking about Bowman. I myself have been thinking about making a rifle, kind of like a barret .50 cal, semi auto, and combustion. I like the size of the rifle, because it gives me more room to work with. Take a look through the show case and discussion, JSR has a combustion cartridge with shell ejection that may interest you. Doesn't use a gas ram, but it uses the force of the recoil to push the cartridge back and eject the casing.
Posted: Sat May 12, 2012 4:23 pm
by Bowman
warhead052 wrote: Take a look through the show case and discussion, JSR has a combustion cartridge with shell ejection that may interest you. Doesn't use a gas ram, but it uses the force of the recoil to push the cartridge back and eject the casing.
Interesting....Maybe if I could figure out a way to "measure" recoil? I know there is a way.... I took a look at the thread I assume you were talking about this:
So, from what I can tell so far. I/we have a few options. We can learn how to measure expanding gases or learn how to measure recoil. To be honest I don't see why either of them wouldn't work.
Posted: Sat May 12, 2012 5:01 pm
by warhead052
Yes, that is exactly what I was talking about. The recoil wouldn't be a hard thing to deal with, simple as adding a all thread bolt, and a nut-fender washer-nut combo to hold the spring in place, and twist it to adjust tension. That way its easier to adjust for recoil, and you could possibly use hybrid cartridges then. And the gas expansion, I am sure someone like DYI or JSR can chime in to help with that.
Posted: Sat May 12, 2012 5:12 pm
by Bowman
warhead052 wrote:Yes, that is exactly what I was talking about. The recoil wouldn't be a hard thing to deal with, simple as adding a all thread bolt, and a nut-fender washer-nut combo to hold the spring in place, and twist it to adjust tension. That way its easier to adjust for recoil, and you could possibly use hybrid cartridges then. And the gas expansion, I am sure someone like DYI or JSR can chime in to help with that.
GENIOUS!!!!!!!!!!! haha anyway, yea I think you're right about recoil being easier to measure then expanding gases especially if you can adjust the springs tension.
Posted: Sat May 12, 2012 5:48 pm
by warhead052
Yep, plus it will make it able to control rate of fire on semi (Stupid maybe, but useful. Allows time for the barrel to cool if you are firing rapidly).
Posted: Sat May 12, 2012 7:46 pm
by Bowman
warhead052 wrote:Yep, plus it will make it able to control rate of fire on semi (Stupid maybe, but useful. Allows time for the barrel to cool if you are firing rapidly).
Sounds good I'll see if I can get some animation up soon.
Maybe I'm late to the party but here goes: For recoil- or gas-operated systems, you get a lot of force for a very limited time, which can be difficult to handle.
My idea is to use this force to tighten (stretch or compress) a spring, and nothing else. I think a long stretch-type spring from a table lamp, or some sort of rubber band, will work the best. When the spring has been stretched and the energy from the recoil/gas spent, let the spring itself perform the actual work (metering, reloading) on the return stroke.
This way you always have a predictable force operating your mechanisms, and they can work at a slower pace since the energy doesn't disappear until the spring has returned. Any excess force can be absorbed by a bumper or similar once the spring has extended the appropriate distance, so you can have a large margin between the force necessary to operate the mechanism, and the force actually produced, leading to reliable operation and room for tweaking.
Most of the mechanism can also be tested without actually firing, by manually cocking the spring. The only live fire tests necessary are to determine that the force produces is large enough to actually cock the spring. Another advantage is that if the fuel/reload mechanism was to jam, destruction is less likely since the jammed part only has to absorb the spring force, not the full gas/recoil force.
For full auto, both recoil- and gas operation has the advantage of not cycling once the ammo is spent, depending on construction the gun may fire one blank charge before stopping. A provision for manually cocking the spring would probably be useful.
I got this idea after seeing my airsoft semi split BBs in two during a jam, and break the reloader when it jammed on an alu BB. This mechanism was a bit different, being connected directly to the main piston in the piston valve (pneumatic gun), but it also had to deal with large, sudden forces. I've never actually built a cannon using the ideas laid out above.
