I agree VERY strongly about using only 3" for hunting applications. The 2 1/2" shells are just too weak for hunting, you'll "jump" more rabbits than kill and wing more birds than drop, it's just not worth it. You shouldn't notice any problem shooting 2 1/2" in your 3" chamber. Maybe check out your chamber shoulder every now and again, to make sure you aren't catching anything on it and tearing it up, otherwise, I'm sure you'd be fine. Heck, good luck finding anything longer than 2 1/2" in slugs, so obviously they must not think it's going to hurt anything.

Screw the 10 ring, keep them in the zero!!!