It seems I have led a very sheltered life as I have never seen or heard of IMR 7977 or 4451 either. When I first started reloading in the early 70's I bought a Nosler reloading book at Ellwood Epps, read it, bought some IMR 4350 and a box of 165gr. partitions, loaded up some and went to the range. The M-70 push feed would put 3 in a group the size of a quarter on a fairly regular basis if I did my part. It even made a nice clover leaf three shot one hole on two occasions. I remember thinking, that was fairly easy. Only ever shot the rifle a bit before hunting season, so for the next 30+ I never seen reason to experiment with anything else. That load and rifle worked well for me. I was shot gun man mainly, as I shot thousands of rounds at trap, skeet, then sporting clays.
Only started expanding my horizons with rifles and reloading for them after I retired, I have learned a lot and do not consider myself overly knowledgeable on the subject yet.