I wonder if the buildup of plastic in the chokes might tighten the patterns if not properly cleaned. I've noticed that the buildup is particularly severe in my Guerini 28 gauge for some reason, but the choke tubes are easy to remove and soak and then run a brass brush on a handheld electric drill through.
I have put over 1500 rounds through my 687 SP II Sporting in three hours and never noticed that the patterns tightened discernibly, shooting doves. The plastic would build up in the extended, and ported, chokes I was shooting, and a stainless steel tornado brush on a short handle would quickly remove it before the next shoot. I also cannot prove it doesn't tighten the pattern some, but when you're shooting that fast it's hard to notice. I was using IM and IC chokes most of the time.
Good question, R40X
