Up until recently I had a British .410 hammergun. It was proofed .410 for 2-3/4" shells. The other thing odd about it was that the upon firing, the shell case would swell enough that I couldn't fit it into my other .410 which was a Nitro Special. The British hammergun had proofs and reproofs up to 1989 for the latest. I always figured it was intially a .44XL.
Steve

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