375Brno, I had the Father In Laws Greener SxS shotgun opened up to shoot steel shot had the forcing cones lengthened from 3/8" to 3"inchs long the choke's I had opened up to Modified and Modified (1/2 choke) been shooting it all this duck season with no problem's at all. The gun is rated at 3 1/4 ton / square inch. The only cryterior that the gunsmith was concered about was that the bores had to be greater diameter than .729 thou of a inch. Pretty much got sick of steppin over it in the gun room and not using it.