Q: Recently I bought an old Ruger M77 MK I with tang safety at a gun show. It is chambered for the 7mm Mauser cartridge and the bore appears to be in good shape. However, I struck some serious accuracy problems when I started reloading for this rifle, particularly with light bullets from 120 to 140 grains. The guy at my local gunshop told me that the 7×57 isn’t very accurate with light bullets. As I don’t intend to load anything heavier than 140gn spitzers, is there anything I can do to improve accuracy?
A: When introduced, the 7×57 was loaded with a very long 175gn round-nose bullet. This required a very long throat ahead of the chamber to accommodate the long projectile. Sporting ammo was likewise loaded with a long bullet of 175 grains and most European ammo contimues to be loaded that way even today. Because of this factory 7×57 rifles have the same long throat today. Because lighter bullets are shorter, they must travel through the throat for up to 7mm before engaging the rifling. Because of the high velocity the bullet gains before contacting the rifling, the bullet often becomes deformed ever so slightly – enough to ruin accuracy. However, I reviewed one of those early Ruger M77s in 7×57 and found it was nowhere near as well made as later models.
The barrel had a .2856″ groove diameter, the chamber was oversize and the throat was long enough to be truly called “freebore” even with 175gn bullets. I found I could use hellacious powder charges without getting anywhere near what could be had with a better made rifle. Seating bullets farther out in the case neck will help reduce the freebore area that the bullet must cross before engaging the rifling. This way the bullet sustains less damage and accuracy may improve. By the way, the 7×57 is a fine cartridge. It’s well balanced and powerful, yet has light recoil and is generally accurate. It was a favourite calibre with Jack O’Connor and Prince Abdorreza Pahlavi of Iran who use it successfully on game up to wapiti. He used Canadian Dominion brand ammo loaded with a 140gn bullet exclusively and said that heavier bullets weren’t near as good killers. Personally, based on power and performance a good 150gn bullet should be the heaviest one should use in the 7×57. Good luck with that old Ruger.