All pre-64 actions are the same length. The various calibers were accomodated by longer bolt stops and blocked magazines for the shorter cartridges, and shorter bolt stops, longer magazines and corresponding magazine wells in for the H&H Magnums.
The H&H actions also have a slight indentation in the receiver ring and a modified bridge to allow ease of loading for the longer cartridges. This modification does not weaken the action and it is not difficult to do with the proper equipment, using an original Magnum action as a pattern.
