in paintball guns, the paintball seems in any cutaway ive seen to be struck by a piston/bolt driven forward by

Question

the compressed air/c02. this impact drives the paintball out the barrel. my question is why isnt the paintball driven by say a butterfly valve opening and allowing the gas to expand and push the ball out the barrel. it would seem more efficent to have the ball driven by direct expanding gas, like a car piston, if you could get the sealing right. rather than have it struck by a piston, and deal with frictional losses, etc. can someone explain to me what im missing?

Answer 1

There would probably be allot of ball breaks in the barrel.

Answer 2

There are a couple of reason for having a "bolt" instead of just using a butterfly valve, without getting to technical. The bolt acts a in a way of keeping the paintballs in the hopper out of the way until it returns to its original position after being fired allowing another round to fall into place. I would imagine the problem you would run into using the other set up would be to many balls falling down into the barrel at once which would result in a action that is normally referred to as "chopping paint". Another reason a bolt is used is for the principal that there are different types of bolt's that allow restrict air flow passing through them in different way, for example the standard bolt just had a hole in the middle of it allowing air to pass straight through when the gun is fired, but other bold have different hole configuration that can ad spin to a ball increasing its stability during flight and improving accuracy, it isn't actually the bolt striking the ball that shoots it it is the air passing through these holes, whatever the configuration, that actually propel it. hope it helps

Answer 3

I'd guess at a couple of reasons, not big enough to prohibit such a design, but likely to add difficulty.
1. Sealing a soft moving ball would be tricky since it would tend not to push any dirt forward like a hard cylinder but would press the dirt against the barrel.
2. A tightly-fitting ball risks tearing its skin with unpleasant consequences.
I did find one design where it appears that the moving bolt only serves as part of the valving system (ref.) but my interpretation may be wrong.