The only shotgun I've really done a bunch of bbl length attempts is the 12ga 303 Beretta I bought circa 1990ish. I've shot 22, 24, 26, 28, and 30" bbls on that same action/stock. I shoot the 26" the best of the bunch.
I have 2 30" 12 and 2 30" 20ga Beretta 391's. In both gauges, the 30" bbls make me lazy over time. I swing less with my body, more with my arms and fall behind. When that happens, I move back to my Franchi 26" AL 48 28ga that's so light it forces me to get back in the habit of swinging with my whole body. A few years ago I picked up a 26" Beretta 626 20Ga who's "shortness" of OAL also snaps back my "whole body swing" form almost as good as the ultralight Franchi.
