The Savage 720 was made c. 1930 - 1949
Savage/Stevens doubles, pumps and SAs were advertised as having some variant of 'High Pressure Compression Formed Steel Proof Tested' (sometimes 'With Nitro Powder')
The 620 in the 50s was listed as 'Special Alloy Gun Barrel Steel Proof Tested'
It is probably safe to assume that the barrels of the 720 were not then 4140.
No one is going to recommend steel for pre-WWII A5s, M11s or 720s, but steel loads today do have thick plastic shot cups to protect the barrels. Using open chokes is of course critical.
There is another concern about the non-compressible steel shot causing microfractures in the shorter forcing cones of that era, and it is my (and certainly other will disagree) opinion that lengthening the forcing cones is a reasonable idea when forced to used steel shot.
IMHO dealing with the frustrating reality of steel shot mandates is worth using these neat old guns.
