SpudFiles

What would happen if you had a large (several litres) chamber that only had a small vent to exhaust out of? I'm thinking (if the word really applies) combustion burst fire BBMG here

Would the hot gasses have time to cool and lose pressure?

Yeah, it would work, but I doubt you'd get the same power equivalent out as you would if you shot a single large projectile. I haven't done the math, but you do loose heat energy from the combustion gasses the longer they stay in the chamber. I think it's "worth a shot" though, not very complicated!

jackssmirkingrevenge wrote:What would happen if you had a large (several litres) chamber that only had a small vent to exhaust out of? I'm thinking (if the word really applies) combustion burst fire BBMG here

Would the hot gasses have time to cool and lose pressure?

Why would you want such a lopsidedly large chamber size for a BB sized barrel?

I have severe doubts this would work. The combustion gases lose their temperature very fast - they have little mass compared to the walls, grammes compared to kilos.

Think in terms of a completely closed chamber. The combustion pressure fast dwindles to nothing, you're not left with a chamber full of any more than mildly warm gases after that first instant.

You might get quarter second bursts, but I wouldn't hold out for any more than that.
After about half a second, the temperature of the gases will have dropped back so far that you won't be able to do anything with them.

Like Ragnarok said, the heat loss is too fast. For a typical size closed chamber the pressure will drop by 50% in 0.1 to 0.2 seconds. By one second after igntion the chamber pressure is basically back to atmospheric.
(From here.)

But it will surely spit out a few BB's before the pressure drops to zero.

I think it should work, the question is how long of a burst would it give.
I think if you set it up with a vortex block or cap it should work decently, you would just obviously have to refuel it after each burst. For fast refueling I would use pre-metered propane "cartridges" similar to what someone did when they made the triple thunder advanced combustion guns.

psycix wrote:But it will surely spit out a few BB's before the pressure drops to zero.

"A few" being the important phase. Lets see, at 50 RPS (typical BBMG). Figure you have decent pressure for 100mS followed by another couple hundred mS as the pressure drops down. That'll give 5 rounds at high pressure. Small ID of the barrel is going to suck heat out of the gas flow like crazy, so figure you might get another 10 or so BBs before the pressures gone.

Be interesting to see if it is worth it. Off hand I would think just putting 50 BBs in a sabot and firing'm like a shotgun shell would be easier.

jimmy101 wrote:Be interesting to see if it is worth it. Off hand I would think just putting 50 BBs in a sabot and firing'm like a shotgun shell would be easier.

That's basically the conclusion I reached

jimmy101 wrote:Off hand I would think just putting 50 BBs in a sabot and firing'm like a shotgun shell would be easier.

I've been longing to do this for quite some time. I was thinking something like skeet/clay pigeon shooting with two launchers, one with BBs, one with water balloons...