What are the rebuild marks?

[NRAchad]

[GPlourde]

I'm sorry, I stated it was BA4 5/64 should have been 5-66 on HRA 4721XXX.

[finloq]

Sorry to ressurect the dead here. But These marks would only be present if an Arsenal rebuild occured, correct? For example, my 1954 HRA still has the original barrel (presumed due to barrel date coinciding with serial range). Can I assume that while being rebuilt (probably by the Greeks and again by the CMP), it never went through a full arsenal rebuild.

[Joe W]

Correct, the code would only be found on the receiver leg if your rifle was rebuilt at one of the Arsenals. I wouldn't call changing out some parts by the Greeks, CMP or even the U.S. Military a "rebuild" or an "overhaul".