It could have been "loaned" to any of our allied countrie then returned to U.S. via Fed. Ord. importers.

The most likely cause for no rifling at the last 3/8" of the barrel is excessive cleaning with a cleaning rod coupled with improper use of a cleaning rod. The rifle may have been used at ceremonies firing blanks and left uncleaned long enough for the inside of barrel to deteriorate. Whatever country it was in may have used corrosive primer cartridges.

The rifle could have been used for training purposes excessively and thus shows excessive wear. IHC rifles are in high demand, esp. if all parts are IHC.