George,
I haven't experienced that to any notable degree. But it seems reasonable in theory, since more percentage of the shot load is in contact with the bore/forcing cone/choke than with a 2 1/2". Shooting a 3" shell in a 2 1/2" chamber would certainly make for a few reactions likely including a pattern effect, among other things.
In actual practice, I've seen a noticeable tightening of the pattern by cutting very long shallow angle forcing cones and polishing them. I attribute this to less damage to the shot.
Last edited by Chuck H; 10/01/12 03:44 PM.
