With the availability of great 2 1/2 inch shot shells online, why would you use anything other than what the gun was designed for........?..........
I think it is wrong to use anything larger than the ammunition the gun was designed for no matter what Sherman Bell says.......other opinions around here will vary........
Here's two ammo companies that supply new "off the shelf" 2.5" low pressure loads for vintage shotguns to folks that don't reload........and one of them is almost in your back yard......
http://polywad.com/http://www.rstshells.com/store/I reload all my own and always stay below 7,000 PSI for my older 2.5" guns and use the same 2.5" ammo in my newer 2.75" guns as well......2.5" in 12,16 and 20 gauge guns......birds don't seem to know what they've been shot with, they just drop dead.....