I have a field grade 28" 12 ga with US stamped on both barrels and appears to have a difficult to read USA stamped on the left barrel. A friend of mine gave the Smith to me a number of years ago knowing that I had a small Smith collection. He told me he was given the gun by a friend who was in the military and it was used to train gunners assigned to WW II bombers. Looking for any insight. From the SN it appears the gun was manufactured in 1940.