ALWAYS pattern a gun before making modifications. #3 steel is a nice size for fixed choke barrels and you might like the pattern it throws as-is. I hunted with 2 1964 Browning Auto-5's for years with fixed full chokes even using BB steel in the early years before they really knew how to protect the barrel with good wads. Never had any issues at all out of those guns and hunted them hard for probably another 20 years after steel was required. No belling at the choke and no scratches although the Browning barrels might be a bit better quality than the Russian guns I do not see why you would have an issue eith #3's. In a full choke O/U I would stay away from larger steel shot just in case it does expand at the muzzle it could break the rib solder joint between the barrels.
CPL holder since 1991, NRA Lifetime Member, DU Member, NICET certified
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