Am I correct in saying that P guns are built on 12, 20,28 and 410 actual frame sizes?
Mike; I don’t know the answer to your question for certain, but Karl Lippard’s book ‘Perazzi Shotguns’ circa 1994 describes the MX20 as “small frame”, the MX28 as “very small frame” and the MX410 as “very small frame”. He makes no particular distinction in frame size between the 28 and .410, but that was also in 1994.
Shoot them an email, Mike. I'm sure they would reply with that information.
SRH
I am pretty sure that there are three MX-8 family frame sizes: 12, 20 and 28/410. Smaller barrels are often fitted to larger frames, 20 on 12 frame, 28 on 20 frame, etc,