Thanks to everyone for all the input.
The under rib is open at the end, and it is flush with the end of the barrel. Also, there are no decorative features at the muzzle, (stars, circles, etc.) and that led me to believe that it had been shortened. Perhaps whatever had plugged the end of the rib fell out. The rifle is very heavy as it is, and it would be even heavier, if longer.
George