Vicious-V

Damn, haven't been here for awhile...I hope this is Nerf-related.

I'm going to be building a tennis ball mortar. It'll use a 100lb. spring. The cocker will have a foot pedal so I can just stomp down on it to cock it. The whole thing will be made out of metal. I have a few questions though.

1) What should I use for the trigger catch and trigger system that can handle a 100lb. spring?
2) The tennis ball fits pretty tight in the barrel, will the plunger be able to propel it?
3) What should I do to make this airtight?
4) What should the size of the plunger be for maximum performance?
5) What should I put at the end of the plunger so the slam won't snap apart the whole thing?

Thanks...

Does the LBB use a piston valve? The trigger pulls that rod so I'm assuming it pulling the black rubber disk you see when you look down the barrel, just like a piston valve.

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How many FPS can a blowgun hit BB-wise? Are they able to go up to 100 FPS?

Any of you know any remote controlled cars or planes that go at a decent speed but cheap at the same time? About $20-$30 limit. Maybe 20-30mph?