I will try Teflon tape and maybe use a friend's vice if wrenches don't work. Otherwise I will try liquid sealant. So liquid sealant can be removed later?

I wrap the tape in that way but it still leaks. How do I tighten it more than by hand? I don't have very many tools available and no workbench with a vice.
I guess I will try the pink tape though.

Sorry if this is a really dumb question, but I just assembled my first metal cannon but cannot get it to stop leaking. First I tried regular Teflon tape then I tried the yellow Teflon that is supposed to be made for metal pipes. I went through a roll of each after trying repeatedly to get it to seal ...

Where would I get the metal pipes or something to use in their place?

OK thanks that will be easier and safer than trying to make a burner

Would a regular propane grill be able to reach at least 400-500 degrees Fahrenheit?
Like a camping or other portable grill?

Yeah that second image would work great but what parts could I use to make it?
I am pretty limited on tools and usually just use my hands, a drill, and a handsaw.

Thanks for the suggestion

I have always wanted a gas powered airsoft rifle because compressed air is just so much better that the mechanical power of AEGs.
Polarstar finally made something available that is similar to what I want but sooo expensive :(
I may invest in a Polarstar later but for now are there any other cheaper ...

I have most of the parts now but I am re-thinking the exhaust hose.
I have pressurized hose from Lowes and was going to just thread it into the back and wrap it around to sit on top of the cannon. Instead I am going to use 2 90 degree elbow pieces.

Also I am not sure about a valve I bought on ebay ...

I was thinking of putting styrophome or something soft to stop the piston.

I don't know where to get and o-ring that size and how would you hold it in place anyway? Is it a lot simpler? I am still getting the parts together to make this and could use that instead...

But also instead of nitrile ...

I'm not worried about the piston not moving- if It jams I'll use silicon oil or grease but I will try the hard rubber with nitrile rubber gloves

2" chamber and 1" barrel

the piston will fit into a 1 1/4" pipe

Should I use this rubber or find something better? if so where would I find it?

silicon oil where the rubber meets the barrel? won't that dry up?

Will these parts work for a 1" barrel?
Its a 3/4" PVC cap (a bit bigger than 1" pipe), a screw and nut, and a "rubber packing sheet" I got at Lowes.

http://i1165.photobucket.com/albums/q590/SomeGuyPerson/air%20cannon%20stuff/20120204_130536.jpg

Anyone used this rubber before?

Thanks

Thanks for all the help!

I have had experience with pneumatic cannons but not with pistons. I will definitely make a battery launcher though- I have at least 40 dead AAs