SpudFiles

I am currently working on a 3" piston cannon, and found out that a skippy peanut butter jar fits quite nicely into 3" pipe, with only about 1/16 of an inch between it and the pipe. The jar is plastic, so I decided to reinforce it with hot glue. My initial plan was to completely fill it, but I only had nine sticks, so I instead just covered the inside with about a quarter inch, with about a half inch on the bottom. What I really want to know is, will this be strong enough? I will have the opportunity to buy more glue tomorrow, so If necessary I could fill it up all the way, although I would have part of it hollow for weight reasons. If I can avoid this though, that would be awesome.

Pics:[/b]

It seems to me you could do with a can of expanding foam. Hot glue exhibits a tendency to malform, and under repeated firings could cause your piston to jam. A lot of stress will be placed on this one piece and as such you need to make it as stiff as possible. It looks like a nice effort though and if it is able to be serviced throughout the life of your launcher i would try it with just the hot glue.
Otherwise make the piston resemble a recently departed living organism (a stiff).

I agree with nova get some expanding foam and make the piston shorter it doesnt need to be that long other than that it looks pretty good so far.

I believe I do have some expanding foam, Should I fill it with that (I think its "great stuff")? It will be servicable, so I could go either way. Also, what are your thoughts on partitioning off some of my most likely large pilot volume with the stuff?
Edit: I made it this large to cut down on the pilot volume, although if it ends up being too large I will just cut some off.

I think you should fill it with the foam. As for the pilot volume we have all been privy to the many threads that exert a strong liking for a small pilot volume, as such i would recommend filling in all the dead space that you possibly can, just make sure that you still have enough flow for proper activation of the piston.

Okay, thanks guys. Expanding foam it is! Now to figure out a bumper...