combustion powered airsoft gun.

[ramses]

I was thinking of trying to make a select-fire combustion airsoft gun powered off propane. This would utilize a blow forward bolt and a spring assisted magazine that would not be replaceable. I have numerous questions about such a design.

1) how would the presence of heat effect the BB. would it melt/deform/stick to the target in it's semi-melted state?
2)after the hot gases left the chamber out the bolt, could the bolt seal and allow air to bleed in through a check valve because vacuum caused by heat loss to the chamber walls?
3)would heat build up from sustained firing melt seats on valves, O-rings, etc.?
4)is such a design worthy of the effort required to design and build it? or should I Build a scaled down version of Clide's GB Semi, power it with propane, and use a wanna Be aspirator on the barrel to get the awesome muzzle flash effects that would doubtlessly be attained with a combustion design?
5)Does anyone know of a cheap source of 3 way direct acting solenoid valves?
6)what kind of Max ROF could I expect from such a system with a large mixing fan?
7)What could I use a a hopup that would withstand the temperature?

[Ragnarok]

1) Utterly negligible.

2) This would be very tricky. I've considered it myself, and it has several drawbacks, chief among which is the limited vacuum pressure.

3) This, unlike #1, could be a problem. If the ROF is high enough, things will melt.

4) That's entirely up to you.

5) No, perhaps Ebay.

6) I have a design of my own that I've predicted to be capable of about 1500 rpm, however, it requires a myriad calculations to be done before any parts are made, and I haven't even finished them myself for my design.

In your case, I have no idea. From what you've mentioned, vacuum vented chambers - don't get your hopes up for more than a couple of rounds a second, and even that would be optimistic.

7) There are high temperature rubber like materials that should suffice.

[Davidvaini]

Also a thing to mention is the fact that most airsoft fields dont allow any combustion's.

It would be a fun little project for a backyard plinker.

[ramses]

Also a thing to mention is the fact that most airsoft fields dont allow any combustion's.

It would be a fun little project for a backyard plinker.

I intended this to be a backyard against the rules type gun.

any ideas on an artificial method of automatically venting the chamber. besides another solenoid valve and a centrifugal blower?

[Tsukiten]

If you have a mini-blowtorch (those blue-flame "stormlighters") you could make a gas-tube system that most assault rifles use.
Gas goes trough the barrel, through a smaller tube back to the gun and pushes against the mini-blowtorch "button" so it releases a perfect air/fuel mixture into the chamber, ready to be ignited.

[i-will]

sounds great. i'm planning the same project but in cartridge form for a one handed revolving launcher i haven't started on yet. the design is great.

go for it.

[ramses]

If you have a mini-blowtorch (those blue-flame "stormlighters") you could make a gas-tube system that most assault rifles use.
Gas goes trough the barrel, through a smaller tube back to the gun and pushes against the mini-blowtorch "button" so it releases a perfect air/fuel mixture into the chamber, ready to be ignited.

interesting idea. i suppose I could do the same with a propane torch and just hook up a solenoid valve in series with the aspirator. the only problem is that the tip is essentially a tube with holes in it, so any pressure build up would be wasteful, but not nearly as much as using several cubic inches of propane in a pneumatic design. Excellent idea, time to think of how to implement it!

[Tsukiten]

interesting idea. i suppose I could do the same with a propane torch and just hook up a solenoid valve in series with the aspirator. the only problem is that the tip is essentially a tube with holes in it, so any pressure build up would be wasteful, but not nearly as much as using several cubic inches of propane in a pneumatic design. Excellent idea, time to think of how to implement it!

Thanks
I'm gonna try building something working on such next week, since I have a full week no school then.
But when you think about it, it might not be as easy.
In order to get it to cycle you need sufficient pressure in the barrel = a projectile needs to be in the barrel.
But to do that, you need to have a breech which then ammunition is fed through by a magazine.

[ramses]

no-one says the gas rod that pushes the button has to be on the barrel. for 6mm, that wouldn't be a great option, so you just connect it to chamber, where pressure is choked by the 6mm barrel. the breech could just be copied off someone else's work. just search "semi auto breech".

[Tsukiten]

no-one says the gas rod that pushes the button has to be on the barrel. for 6mm, that wouldn't be a great option, so you just connect it to chamber, where pressure is choked by the 6mm barrel. the breech could just be copied off someone else's work. just search "semi auto breech".

I'm kinda worried the gas would be ignited as soon as it enters the chamber, because there might still be some reactions going on.
But yeah, we've just gotta try it out.
Also, I wonder how good blow-forward breeches would perform on combustions... o.o

[ramses]

you bring up a good point about the instant combustion. I say use a 555 and a solenoid valve between the fuel regulator and aspirated burner. the blow-forward breeches, I think, would work fine if heat resistant with heat resistant O rings. O rings might not even be necessary because there isn't any pressure to contain. it'd be nice if you could machine the needed parts out of aluminum. with the 555, one could vary the pulse-width to use the minimum amount of fuel/air mix. in theory, by using a shorter pulse width, you could, to a point, turn down the muzzle velocity.

[rp181]

say you used a TL494, pulse width matching that of the correct mix, you could inject air first, which would allow time for cooling before propane goes in.

Or... Stick a heat sink on the side =)

[nibbler125]

i wouldent worry about a airsoft bb melting unless you are shootin constantly untill youre gun starts to heat up

[ramses]

I dont think it is a question of heat buildup, but of injecting the mix into a chamber while the last charge is still burning. this could be solved in a number of ways: reduced ROF, chamber fan and/or multiple ignition points.
Any ideas on a fan able to stand up to this enviroment.

p.s. sry for typos, this was dne on a PDA.

[jackssmirkingrevenge]

It does sound a little overly ambitious, but again, look to gas powered nailguns for some inspiration.

Have a look at this little animation, click on the trigger to make it function.

Loving the signature btw *chuckle*