From what I've read, by the early 1980's steel walls in shotgun barrels on most mass production guns were made thicker for steel shot. Of course high end O/U and SxS were not made that way unless the maker states so. I shoot Japanese Brownings with steel (IMP and MOD choked only) and steel in a 1974 Winchester SXM1 MOD barrel, but never in my Belgian Browning's or Pre-64 Winchester's. It can be frustrating to research; as an example, currently Browning only states steel is okay in Invector barrels, but prior to Invector being introduced they stated that fixed choke Japanese made Auto-5 barrels were okay with steel. You might want to call Ithaca and see what they say about an old M37.
