Rarest of the rare; built in 1943 as a possible replacement for the M1919 series BMG; the T23 used BAR or modified BAR internals and a belt fed Mechanism.  5 toolroom T23e1's were built, 3 were modified into T23e2.  This is the barrel from the first T23e2 (without Flashhider).  Unfinished, as it came from the Colt storeroom in the 1970's