for the Keltec PMR-30, I am thinking a threaded barrel, or an extended barrel, extra 3/4 inch. I think just a bit longer barrel will assist in a better shot/higher muzzle velocity/and better recoil/reload. Keltec has a “PMR THREADED BARREL WITH MUZZLE BRAKE”, but not in stock, and no expected delivery date.
Also, since I could never get the extra power recoil springs installed, how about the whole thing ready to drop in replacement, instead of the wire on the end holding it all in place, a c-clamp type of piece, to make replacement easier?
On a side note, sounds like a good idea for the Ruger 5.7