Good luck David - 1 in 20 is a good twist for 500gr. bullets in .45 calibre. Larger bores require slower twists as even a .50 cal. with 24" will handle bullets over 650gr. From my meager experiance, a 20 bore should have around 46" of twist for short conicals and 56" TO 70" for round balls.
: 12's, which will hold up to 190gr. 2F and round ball in a 2-1/2" case is better served with 80" to 100" of twist, fastest around 70" perhaps.
; I hope yours is OK.
; PacNor makes find barrels, as you already know. I am surprised they made a 12 bore with that twist. Might work find with 1,000 grain bullets.
; Very nice gun, just worried about that twist. With really low velocities in the 1,200fps range, it might be OK.