Can you give us a little hint of what you are making?
Okay, since you asked nicely (and since I'm not going to get to finish it tonight) here's a peek...
When I saw the very first micro-gonne, I said I was going to make one. Well, it's took me awhile to get around to doing it, but I finally got the major machine work done today.
It still needs a vent, final polish, and bluing. I had forgotten that I broke my 1/16" drill bit until I got home and started looking for it. So I'll have to make a trip to the hardware store tomorrow. I haven't decided yet whether I'll drill the screw hole in the tiller socket, it'll probably depend on what I use for a tiller and how it fits.
I really wanted brass, but I have good steel scraps free for the taking, so steel it is. Sorry there's nothing for scale, but I was in a hurry (when am I ever
not?). The overall length is 4", the major diameter is 9/16".
It has a 1/4" diameter bore, and a 3/16" diameter x 3/8" chamber. Total depth including chamber is 2¾". The tiller socket is 3/8" diameter.
With the 3/16" chamber, it meets the "one caliber" rule.
It will fire a #4 buckshot pellet, which has a nominal caliber of .24" (they actually measure slightly less than that). I included some pellets in the photos.
Why #4 Buckshot? Well, as mentioned, the size of the pellet allowed me to use a standard drill for the bore. Also, I have more of them than I will
ever fire in this gonne.
I laid in a stock of cheap Estate 12 ga. #4B "SWAT" (low recoil, reduced payload) loads some time back. These are okay for practice but they burn very dirty. I have a lot of them left, each shell yields 22 pellets, and they were cheap enough that I don't mind cutting a few of them up. And best of all, they're already paid for.
The gonne was based on this design (with a few minor liberties taken during machining):
When it's finished, I will take some better photos (with proper scale reference).