That is a unique piece for sure. The receiver is proper for a 48 transitional H&H; some were undrilled, some had one hole and some had 2 holes D&T on the rear bridge.
I have seen numerous M70 barrels with 5 characters (1 letter and 4 numerals) in addition to the standard marking for special orders and return repairs/rebarrels etc. 300M 48 is how a 1948 300 H&H is marked.
Very true.. My only caveat is the tag and the sales clerk said it was a .300 Winchester magnum. Which is a different animal (obviously) than the .300 Magnum which, at the time, referenced the .300H&H as you stated..
I was thinking the same thing regarding the special order markings. Roger Rules book indicates that. The store didn't know what they had IMO. The crazy thing about this whole deal is that I was in the store to pick up another 300 HH with a 88,XXX SN. We laid the rifles out together and compared them, I even had them take the rifles out of their stocks to look at the barrel markings. They had no answer other than "wow that is interesting".
The proof mark is the big mystery. Is it a PW or a P? The P is a mail order replacement barrel.
The receiver has been reblued or it appears that way due to digicam images of gunmetal.
It would help to see the under barrel marking to see if it is original or redone. Look hard at the breech end and see if there is evidence on a 2d extractor cut (possibly filled) at 6 O'clock.
Also did you try and chamber 300 H&H in it? Many times smiths just rechambered the 300 H&H to 300 Win Mag without setting the barrel back.
Or the .300 Wby..
The proof mark is PW I have not tried to chamber any rounds into the rifle, but I will today.
I don't believe that the receiver has been altered or re blued.
Let me know what you find as far as my questions.
Yeah, me too..
