It is one thing to do somthing that may hurt or kill yourself in private. But to take a chance and do it with bystanders that assume this is safe. I think not. I have done a LOT of dumb things in my teens.By the grace of god I am still here. We must,in public be as close to 100% as we can with safty.I would not use your pipe volley gun anywhere near anyone.
Gas pipe is black pipe.Made of with a welded seam.It is made to hold lowpressure gas at 10 lbs pressure.Or up to 200 lbs of air pressure.Sure there is a safty factor built in.It may hold to 5,10,or 100 rounds,It may not. I would use seamless mechanical tubing. It can be had in all common sizes from a good steel supplyer.This in 3/8 wall is what is used to line C/W cannon tubes.I expect that 1/4" wall with a .5 bore would be safe. This is just somthing you can not be "cheep" about
My .02
Jim Weber Btry C 1st Mi.Lt.