that pps adapter is 1" (the round (not hex) ones I've bought from pps all ended up being 1"; hex od is larger)
EDIT: after actually reading the OP's full post... I have actually done exactly what you are doing! Ran a 12g via 1" scope ring and CA -> 1/8th npt. No problem, works fine.
Last edited by toymachine; 09-27-2012 at 10:39 PM.