Check out the last page (14) of the Superposed Owner's Manual; No. 8 regarding chamber cleaning
https://www.browning.com/content/dam/browning/support/owners-manuals/superposedmanual.pdf Some Browning patent Fabrique-Nationale-Herstal very early versions of the A5 shipped to the U.S. between 1903 and 1909 are marked Cockerill Steel. “Special Steel” began to appear on A5 barrels in the mid-1930s; the Sweet Sixteen, introduced in 1937, barrels were so marked. The Superposed, introduced in 1928 had “Special Steel” starting about 1948.
I have no information as to the composition of "Special Steel", but it was likely non-alloy AISI 1040.
