Although your rifle says "FTR 57" - ie "factory rebuild in 1957" - it was probably never actually "rebuilt", but was a brand new rifle that was inserted into a batch of FTR rebuilds in order to make up numbers or replace something that was scrapped. Most of the rifles marked in this style show no evidence of having been refurbished from an older rifle. E.g. from the photo, it appears that the receiver is the late-pattern Mk2 version with no cut-off boss on the right side.