i confess i've never once actually measured that distance. from the crook of my elbow to the first joint of my bent trigger finger is actually about 13.75". maybe 14" but not more but that's fibbing. i like LOP to be at least 14.5" and 15 is fine. straight hand guns 15 at least. i will also admit tho, living here, that i very seldom have occasion to shoot in anything more than a light jacket so bulky clothing isn't an issue. the last model 21 i had was only 13-7/8 over a non-original pad and i couldn't hit squat with it. the crescent arms i got from my dad is more shootable. my model 11 is 14" even over an non-original pad and it works fine. the curvature of the grip has a tremendous about of influence on what length really works. but out of about 30 shotguns (i trade a lot) over the last 3 yrs that i've been keeping track, the longer the LOP within reason the more easily i can hit with it and the greater the pitch the more i miss.
roger
