Griz
I have an old British .410 hammer gun that was proofed for 2-3/4" shells. I lengthened the forcing cones and shoot 3" shells through it all the time with problems. BTW the gun may originally have been something else, I say this because when I shoot it the shells expand enough so that they wouldn't fit into a 410 Nitro Special I used to own.
Steve

Approach life like you do a yellow light - RUN IT! (Gail T.)