Interesting... My H&R65 came to me from a WWII Marine vet who was on Guadalcanal and then thru the islands. A demolition man, he re enlisted after the war for another hitch.
Mine has USMC stamped right above the SN (46XX). Both serial and USMC look similar in age
I.E. the USMC does not appear bright inside the stamping. He said he brought it home after he got out.