By Mark V. Lonsdale
Can a big bore, belted magnum, dangerous game cartridge produce the same accuracy as a precision long range rifle? Absolutely, but the rifle must be built to the same demanding specs as a precision rifle. Where 2″ at 100 yards can be considered acceptable for an off-the-shelf factory hunting rifle, long range precision shooters are looking for not just sub-MOA but 0.5 MOA. In practical terms, 2″ at 100 is 4″ at 200 and 6″ at 300 yards, well within the heart and lung kill zone on a large animal. But once a shooter has been bitten by the precision shooting bug, only super accurate rifles are interesting.
For this project the rifle was built the same way I build my long range and ELR precision rifles. This begins with a Stiller’s Action, Bartlein barrel, McMillan stock, and Bix’N Andy trigger, topped with a Leupold Mark 5HD 5-25x scope.
Initial break-in with 32 rounds was done with an assortment of ammunition that I had on the shelf from previous .375 H&H rifles and plans to head to Africa. Some loads were over 20 years old and mostly Hornady 270 RN and Speer 270 Spitzer bullets in Remington brass, with Federal magnum primers, and loaded with IMR 4064. None of the components were match grade, the brass was virgin factory RP, the primers were 215s, and the cartridge overall length (COAL) was kept at SAAMI specs or less (<3.600″).
Needless to say, I was not expecting anything great out of the first range session. Groups ran 1.5″ to 2″ which is adequate for hunting at close to medium range, but definitely not in the class for precision long range shooting. However the goal was just to break in the barrel.
After giving the bore a good clean it was time to get serious. I had measured the chamber and knew that loading to SAAMI specs of <3.600″ left a jump of almost 0.200″ to the rifling, depending on bullet ogive. That is two hundred thou as a opposed to the general starting point of twenty thou (0.020″) off the lands. This prompted me to begin with a COAL of 3.650″ and 3.700″ since my magazine box could handle a COAL up to 3.825″
As for bullets, I loaded up Hornady 250 GMXs, Barnes 250 TTSXs, and Hornady 270 RN. I also tried Varget and IMR 4350 in addition to IMR 4064. This was still with virgin factory RP brass and Federal magnum 215 primers – and still not match components.
The 250 GMXs with 65 grains of Varget, loaded to 3.700″, had an average muzzle velocity of 2,616 fps and produced a 5-shot group of 0.7″
The Barnes 250 TTSXs with 65 grains of Varget, loaded to a COAL of 3.650″, had an average MV of 2,586 fps and produced a 5-shot group of 0.7″ with best 4 going 0.5″
The Hornady 270 Round Nose with 70 grains of IMR 4350, loaded to 3.600″, turned in an MV of 2,366 fps and a 5-shot group of 0.8″ with best 4 going 0.4″
All three of these loads are definitely in the acceptable range for precision shooting, and still without any brass preparation, bullet sorting by weight, or match-grade magnum primers. So stay tuned for Part 2 when I begin doing more brass prep and utilizing match-grade primers.