Thanks for the compliments, guys
Very nice. Did you grind the threads off the bolt?
Actually, I made the Fire Piston first, then reverse documented construction; the bolt shown in the beginning was the only one I had laying around after the piston was complete. The bolt I used was originally 6 inches long with 2 inches of threads, which I just cut off. A bolt with the threads all the way should work OK, but there might be a long term problem with the inside of the bore being scratched; if you use this kind of bolt, I'd recommend just grinding the threads off.
Sometime soon, I'll have dimensions of everything (of the parts, size of hole, etc.). The one thing I know for sure is that the total cost was under $5 - possibly free if your garage is well-stocked.
One other note is that some of the tubes for sale are smooth on the inside, and some aren't. Hold them up to the lights in the store, looking through the inside to make sure there aren't any burrs or anything. If there aren't any which are 100% (as was my case), spend a bit of time polishing the inside; I just 'chucked' a piece of a rag in a drill and soaked it with polish compound.
This design can work without lubricant, but - especially in the beginning - you should put a bit of lip balm, crisco, or spit on the o-ring. (I'd avoid light oils like wd-40 at the risk of creating a one-shot diesel gun).
Go very SLOW while cutting the groove for the o-ring, checking the fit frequently to make sure you don't go to far.
Good luck to anyone who tries it! If you haven't done a lot of this stuff, before, I'd recommend picking up an extra bolt and o-ring or two.
