ball piston?

[pyromaniac]

I dont think the hardness of the rubber matters on a seal, just so long as the sealing face is flat and they seat against each other properly

would it be needed to like makein inside out barrel cutter thing for there the ball seals against. (tapered or inside out tapered im a little confused on that right one to say.) Then the ball will have something righ to seal against.

[Hawkeye]

Yes, bevel the sealing face of the barrel to the same curve as the ball.

[rednecktatertosser]

put some sandpaper around the ball and make the sealing beveled like hawkeye said, go from coarse to extremely fine grit so that the sealing face is smooth.

[goathunter]

On a sealing face the deciding factor is how well the two sides fit together.If they are both perfectly smooth you can get a seal using any material.The reason everyone uses rubber is because it will form to the imperfections and complete the seal.

Hawkeye has it right.
You don't have to have it the same curvature of the ball but a bevel of some sort is a good idea.If the ball was rubber it could warp slightly and form on a straight sealing surface.

[jackssmirkingrevenge]

Why not epoxy a rubber washer to the breech and use a solid ball? That's what I did with the pengun project (though the ball was stuck to a tube, it was still a sphere that sealed against the breech)

[Hawkeye]

A ball faucet sealer makes a good piston. They are usually available in packets of varied sizes in the plumbing section of hardware stores. They are a hard, smooth black rubber. With a little searching you can find metal tubing that they will fit in nicely. Of course they are very small so you'll have to use them in small calibre/high pressure launchers.

[mopherman]

It seems like it would work. The only problem i can see is that the ball gets jammed in the barrrel port and refuses to pilot.