I have a byf 44 (13213 k) with an interesting variation. The serial # is on the 44 dated barrel, which also has the byf barrel shield. All good. The receiver has the expected proofs on the right (2) and left (1) side but there is no serial # on the receiver. The rest of the rifle is typical of the late 44 byf mentioned in the Kriegsmodell book. I wonder if this variation is seen much?