Your gun is one of only about 800 made, so if you screw up a barrel, its not going to be replaced. Your gun was made in the 30's so was never intended for anything but lead. I use Bismuth in mine. 3 1/2" modern factory Bismuth shells are fine, I reload short 2 7/8 Bismuth for ducks as well. So, basically pressure isnt the issue here, the gun is a tank, but the barrels are too soft for stel much less any of the tungsten/steel alloys like heavy shot. With one of those loads if a pellet gets through a wad petal and contacts the bore, bad things will happen. I know folks who shoot steel in older guns after relieving the chokes, but why take a chance.
