Ok. I have added a screw on end cap. Sorry I didn't check the wiki. Thanks for all your help, guys.

I am building my first combustion launcher, and the design looks like this.

3" wide 3' long pvc chamber
5' long 2" wide pvc barrel
Endcap just pulls off
PVC is, I believe, pressure rated, but I don't think the fittings are.

I am wondering
A. Is this gun going to explode
B. If so, how do I fix ...

Thanks, guys. This should be very helpful.

sabot consisting of wax or similar?

I'd think they would slide, but this would help. I am worried about them breaking in the barrel.

Has anyone tried to make slugs out of red jello? I doubt it would be very effective at any range, but I think these would make good makeshift paintballs if they could be got to stick together on their way out of the barrel.

I'm in the middle of nowhere. I don't have a lowes for an hours drive. Thanks, though. If I ever end up there, I'll check. What's the model number of the generic bicycle pump schraeder valve, anyway?

EDIT:
Google Product search turned up some sprinkler valves.
any problem with these?
http://www ...

Well, there are, but they don't have a good selection. I have had a hell of a time with pvc fittings, and the schraeder valves and sprinkler valves were simply not to be had.

Actually, I think I still need sprinkler valves. McMaster Carr has them, but they are really pricey.

Thank you so much. This looks awesome! I can do the trigger mechanisms myself, and if these people don't have 3" to 1" couplings, they don't exist. I'll just do two steps, it's not hard. Thanks again, man.

I am looking for a good source for schraeder valves, sprinkler valves, and 3" to 1" pvc couplings. As for the first two, I would go to spudtech, which is what put me on to this place, but his store is down. I am wondering where he gets his trigger-style sprinkler valves, as I haven't seen those ...