Their is a reason for no bulge on your model 12 barrel; a book written on the famous Winchester Model 21 that included metallurgy of Winchester steel used on the Model 21 that also includes model 70 and model 12 too. Winchester produced the "hardest" steel in firearm manufacturing during pre-64 production. I also shot steel in model 12's that never showed any sign of stress or bulge. I've seen many posts on other forums NOT to shoot steel in model 12's that you will ruin the barrel. That's not true, a Winchester full choke constriction would be too tight for desired patterns while I.C. & Modified chokes for suitable for steel. While I didn't throw anything larger than BB down the barrels.