Texasjack,
The original barrels were 16ga 2 3/4"(70mm).It is very unlikely that you will be able to find them now.They were likely just not turned in by Cpt.Hammer or his family, if he did not survive the war.I guess you could make an effort to find his family;but if you did and they still have the barrels, you would have the hard decision to make-ask for the barrels or return the gun.That is a decision I would not like to make. It's unusual for the factory to actually mount the scope,and they may have had one of the other "Masters" listed on the card do it for them as an "outside job".Of course they would have the ability, and may have done it,but that work would slowdown the production line.The different serial numbers are also a little unusual.While it may differ from maker to maker,my Heym ( also 16/70-7x57R and 16/70+16/70)has the same serial number on both sets of barrels.They were made at the same time, but a third set made later, by the factory, has the same number; as does a fourth set made by Walter Grass.I noted that the "card" had the weight of shot listed, but instead of bullet weight the length of 26mm.I did not check, but believe this to be 11.2 grams(173 grains). If you did not find a 16 in a circle with a 70 next to it,it must be under the forearm, in spite of my previous opinion.
Mike