45/410 (#41C) barrels are 1137 mild steel, same as shotgun and rimfire barrels, all H&R centerfire rifle barrels are 4140 alloy in comparison including the #45LC barrel, you'll have to do some metallurgy research for the difference in strength cuz I have no idea of the specifics. Can't help ya with the rifling comparison cuz I don't have both to compare, but my 45LC barrel slugs .4525" in the grooves and .4465" at the lands.
Tim