It's commonly believed that the rear bridge was D&T around SN 66,300 (post-war)....Some H&H receivers continued to have untapped rear receivers beyond that...front of receiver always had two holes..
The two holes on the side have always been there from day one....
You really need a Rule book. Here are some other questions you will soon have. Keep on learning its addictive.
When did the checkering go from 20 lpi to 18? When did they put mat finish on reciever? When did they stop the big top safety and why? When did they quit clover leaf tang? How many different stippling patterns were used on front sight? When did they go to machine checkering? When did they go to a plastic butt When did they stop making recievers that wouldnt take a stripper clip? How many times did they change the bluing process? What are the main differences of a super grade.
