I ran across one of the Series 28 Trainer rifles today at a gun shop. The rifle was in extremely nice shape, was never mummed, but rather marked with the 1/X and 3 zero in front of the serial number. The bore was plugged with what looked like a rod extending back into the chamber. This was the first time I have seen one of these, and have only read about them in MROJ. Are these Series 28 trainers unique, or fairly common?