Air piston bb gun hybrid

[Sticky_Tape]

This is an Idea I thought of while looking at some pipe and my 4.5mm barrel. Using air to accelerate a piston to compress air to fire a bb. basicly the air replaces a spring. I heard once that if you accelerate a 1/2'' piston at 7fps you coulds get a bb past the sound barreier with a x lenth of barrel. tell me what you think
IF ANYBODY WAN"T TO USE THIS IDEA THEY CAN BUT JUST GIVE ME SOME CREDIT OK?

[VH_man]

Kinda like a Light gas gun.....

It would work better, Actually, If your piston was simply accelerated like a normal projectile... AKA, screw the holes.

And fill the space between the BB/pellet with some kind of light gas, like helium. It will work far better.

I EXPECT some > 1000 FPS figures!

[Fnord]

I'm guessing if the bb is loose in the barrel it will start to move before the piston ever covers the holes. Air behaves differently than you might expect sometimes. Add an oring in the barrel to keep the bb snug until the pressure rises a bit.

[Sticky_Tape]

The holes are so that the piston accelerates with out compressing any gas making that piston have greater inertia to compress the air very quickly once the front of the piston passed the holes.
EDIT: I think it would be better to have a powerful magnet next to where the bb would be in the barrel

[john bunsenburner]

How about using a balsa piston which replace after each shot and using helium,i like the idea of the O-ring rather than the magnet because one the BBis out of the O-ring it is now affected by it while if oyu have a magnet it could still some how affect the bb in some way or another.

[Sticky_Tape]

Using a balsa piston wouldn't allow the air to be compressed very affectively due to the low mass to volume ratio. I don't like the idea of having to change the piston every shot that would be like burst disks. I waqn't to use a magnet because I think a o-ring would have to be replaced after so many shots.

[john bunsenburner]

I just have the feeling that any piston will be smashed to smitherines and thus unding a piston that is cheep and will be replaced any how will be a good idea...

And i guess the magnet will be ok, doubt it ould do anything major, though i still prefer O-rings, its your gun not mine!

[CpTn_lAw]

make an aluminium piston, with a plastic seal. Fill in the space between th piston head and the barrel with a stoechiometric mix of air and gas, and use the diesel effect to make an explosion inside(for above atm pressure mixes, use a burst disc). The o-ring idea is a great one. It will give a verygood compression and when the pressure is too high, the rubber will compress and let the BB fire. It is the principle of air rifles though, nothing really new. + you need to play with the venturi effet, and have a very little bore compared to the chamber.

[Sticky_Tape]

Well if I could have it heavily padded I think I could make it last at least 50 shots which would be better than 1 and it would have alot better power because of it's weight.EDIT: I do not wan't to use any fuels or burst disks I wan't to make it a pure pneumatic.

[newbmatic]

Maybe you could have a burst disk, but instead the piston could have a needle or something on its head.idk. Great ideea though. Good luck!

[ALIHISGREAT]

i like the idea, but what kind of piston run-up length do you envisage and how long would the compression chamber be?

[Gippeto]

Sticky, I think it'll work, you're making it harder, but not impossible.

I would leave the tube intact. The pressure accelerating the piston will keep doing so until the pressure is equal on both sides, and then it will help offset the deceleration force of the high pressure side.

This combined with the momentum of the piston, should give you a substantial pressure boost.

IF you can prevent the bb from moving before the pressure gets high.

The o-ring referred to, may be your ticket to success.

Or try a burst disk.

[Sticky_Tape]

The holes in the pipe are so that I don't need to use a burst disk or an oring. I think this will give a beter pressure boost because the holes in the pipe allow the piston to accelerate quicker because there wouldn't be pressure building at the front of the piston and by making the piston heavier it will compress the air quicker. the compression chamber will be 3'' long and the lenth to accelerate the piston will be 7 1/4'' there was a change in plan I am going to use 3/4'' cpvc.

[VH_man]

I feel still, Very strongly, in fact, that the need for the holes is null.

take a look at Light Gas Guns, Which are used in physics labs to fire projectiles at 3000-4000 FPS. So fast, In fact, that theyre finding F=MA does not apply to all situations.....



Just replace the Gunpowder with an Air cannon and we have exasctly what you have described.

[john bunsenburner]

There is one trouble i see in your meathod: It will be hard to fill the compression chmber with only h2, and a mix od h2 and air will definately ignite under such presures...Use He