My current state of mind would not let me fully digest the OP, but what is wrong with the 21" M2?
Barrel length does not = long range killing power. Sight radius matters not as
the good wingshot looks at the object to be taken, not the "sights"
Not to pat (Pat) on the back, but I set a course record for 5-Stand (Rio Salado) with my
3gun shotgun...a 21" M2.
Now if you WANT something cool, please get an O/U...while you said you don't care for them,
your back will like not having to police empty hulls.
I would contact August M Crocker Fine Guns for his excellent service, guidance and
pricing on a nice O/U.