My guess then would be the recess is too shallow. The quick and dirty solution would be to grind/buff some off the outside of the claw without weakening it too much. After all it's no DGR. But check the recess first for a simple obstruction, like crud or a burr. I'm no gunsmith by any stretch, that's why I start with the cheap replaceable parts.

I will take a stab at this, but I'm not real sure if I am correct but with that established:

The earlier M-77 were not control feed and you can drop a round in the chamber and close the bolt, then the next model that was a bit closer to control feed could also have a round dropped in the chamber..The Mark 2 is a true control feed rifle and one cannot drop a round in the chamber. To modify it, or a Mauser will surly weaken its extraction and thats not good on a DGR nor diserable on any control feed rifle IMO....

BTW it is faster and more sure to mash a round into the magazine and close the bolt in one easy motion, than to try to drop one in the chamber and close the bolt..I have seen many failures over the years of single loading push feeds..It seems in the heat of battle many want to drop a round in the chamber with the gun held leval at the animal or up a bit and the round simply falls out on the ground...

Atkinson,

the Mark 2 IS a true controled feed design, but it is also designed to accept a round dropped right into the chamber. I think Ruger even mentions that in the manual. Of course you're right that the better way is to load single rounds in the magazine as well. The magazine of one of my Mark 2's only holds three rounds, so I load the magazine and then drop another round into the chamber.