Re: I want to legally make my own can
+1 to the silencersmithing section of the Silencertalk forum. There's lots of reading to be done over there.
You need to fill out 2 form 1s, 2 FBI fingerprint cards, and 2 citizenship forms. If you do a Google search you can find that info. Forms can be ordered straight from the ATF. You need to specify caliber, length, model #, and serial # on your form 1. Diameter is not specified, so you can do what you want there. Of course you need to have it signed by your chief LEO or set up a trust. It seems the wait is up to around 5 months now.