With the exception of the 2", I feel fairly confident using 2 1/2" .410 ammo from the American big three. Most .410s, even light British guns, have fairly thick barrel walls. Although US .410s work at fairly high pressures, I think that British .410s probably work at similar pressures. I, personally, wouldn't be searching for boutique .410 loads unless I had a 2" gun.
I agree. I'd get a few dimensions, just for the sake of confirming that the walls are 'good n plenty' then shoot U.S. 2 1/2" if the chambers were thick and of the correct length.
