Greg,
I have wondered the same thing. I have 3 Birmingham A & D .410s, two of them have 2 1/2" chambers and one has 3" chambers. I think mine are all early-to-mid 1930s guns, but I am not absolutely sure. Both of the 2 1/2 " guns are proved for 7/16 oz, while the 3" is proved for 3/4 oz., quite a difference. They are all in the 4 to 4 1/4 pound range, weight-wise, and they all feel about the same in-hand. So that dramatic difference in proof is surprising to me.
I have been looking for appropriate ammo for my 2 1/2" guns, too.
Eightbore, I must be blind this morning, I just googled RST & Kent and did not see any .410 shells listed on RST's website, and I could not find the 2" Gamebore .410s, either...
