It's a cut-down barrel. The one asterisk mark on the barrel means full choke.
It's interesting that the gun has a choke marked barrel for that serial number because only the early made Military 620 shotguns have the barrel choke marks while the later guns do not. The serial number of this shotgun is very high for a Military 620. The receiver should be US marked if it is a Military gun. The Military guns also have P proofs and ordnance bomb marks on the side of the barrel and receiver. I have seen some 520s with the proof P marks on top of the barrel and receiver like this gun, but they also had the normal proofs and ord bomb on the sides.