Looked down the bore and very dark BUT its a four-groove.
Now, under long-term barrel soaking with fresh Hoppes, after six hour with send a FRESH bore brush down bore and see what develops.
Took some photos before the soaking, will post later.
Did the same with a 17 Enfield and that took five days.
Sporterized MIL Stock has a "R" stamped on the flat surface under the front ring, nothing else.
No rebuild stamp after WWII.