The under lever on these guns is called a Lefaucheux action. http://www.littlegun.info/arme%20francai...giraud%20gb.htm
Many of these guns were built by Sauer. It is irrelevant as to the barrel composition, as they all had to pass proof.

I own Husqvarna M51
.
The serial number dates it to 1947. I regularly shoot Fiocchi Golden Pheasant Loads with it.

I purchased a second M51 and had it converted to 45-70.




Pete