Since usually science fair experiments are supposed to be more controlled, i would upgrade to metered propane. With that you could do something with amount of fuel vs. velocity or distance. You could also do something with ammo shape and distance/accuracy.

i use anti static spray. Kicks like hairspray but is cleaner

i dont think one pump will be 590 fps

Yes. They manufacture the pipe itself so that the outside is perfectly smooth and the right diameter, while the inside isnt made with as much presicion. If they made pipe fittings to go inside it wouldnt always fit perfectly. Basically, you need a coupler

No mythbusters ballistics gel is more complicated and requires chemicals that arent usually household. And this stuff doesnt sound too accurate if pimp is a pellet through two inches of it with one pump. Still sounds like alotta fun to mess around with though. Enough that im gunna buy some cooking g...

I have been wanting to make a valve similar to the one you made for a while. I would like to make is accesible too, like an end cap screwed (and not glued) on where you have your reducer for the exaust. The problem is i have no way to make O-ring grooves and i dont know how to seal the endcap with t...

Yeah 20 bucks is pretty good for an all steel valve. I think with a few pictures and maybe a video, you could get some buyers.

http://www.amazon.com/exec/obidos/ASIN/ ... /ref=nosim

I saw this on amazon today and i have never seen anything like it before. It could come in handy for pneumatics when you dont want to have to stay in range of your air compressor.

Did you use O-rings on this valve? I have been wanting to make something similar but i dont want to mess with O-ring grooves since i dont own a lathe.

i think someone told me once that the pressure is caused by the heat and that its only there for a split second. dont hold me to it though

A chamber of 2 cm radius? That definately wont get it 300 yards. But im with bluetooth on this one, if you want it to look like a sniper and be effective you kind of have to make it pneumatic.

If you really wanna get detailed with this it might be better to go with pipe smaller than your barrel and add fins for stability and accuracy. Then just use a sabot. That would be pretty sweet to make a missile replica filled with concrete and a nice paintjob!

I have a friend that just duct tapes one end of a segment of pipe, fills it with cat litter (or sand, dirt, ect.) and tapes the other end up. Then you just wrap tape around it until it fits snugly into the barrel.

one word noname.....string!

i hope your going with a metal chamber too... But with electrolysis you can just collect the Hydrogen and Oxygen in the same place. This mixture will be the perfect e mixture your looking for. Since there is already air in the chamber of the gun that contains oxygen, the mixture will be a little off...