What Is the ‘Best’ Magnum Cartridge
Magnum-itis. Most of us American rifle shooters have it to one degree or another. Its in our genome. And that explains w…
But what surprised me most was the apparent lack of any additional pressure caused by the hotter magnum primers. I had thought that it would ignite more powder faster, causing a slightly higher pressure peak. But no. Average velocity was—in the case of the .30-06—actually lower at 2,759 fps.
Consistency with the .280 AI likewise suffered. ES was broader (though still not bad) at 35 fps, and SD measured 12. Accuracy decreased, jumping from 0.88 inch to 1.32 inches for the average of the three groups. Also intriguing to me was that the vastly different powders (similar in burn rate but of different chemical compositions) demonstrated similar reactions. Both powders were very consistent with standard primers but rather less so with magnum primers.
Although a test comprising two different powders/loads in two different cartridges is anything but an exhaustive, all-encompassing experiment, I’m still comfortably assured that for most purposes standard primers are the better choice for standard-capacity cartridges in the .30-06-case family rather than magnum primers.
The test spanned the spectrum of such cartridges, using a near-maximum load in the classic and predictable .30-06 on one end and a near-maximum powder charge in the hot-rod .280 Ackley Improved on the other end. Burning more powder isn’t really an option and thus isn’t likely to change the results.
Shooting lighter bullets may allow a couple more grains to be squeezed in, but lighter bullets tend to prefer faster powders, and in my experience faster powders like standard primers. Plus, with a lighter bullet you risk having the projectile bumped forward by the small but enthusiastic detonation of the magnum primer, which can move it in inconsistent amounts each shot before the actual propellant ignites and horsepowers it down the barrel.
One element I was unable to include was the effect of cold temperatures. Another rule of thumb suggests the use of magnum primers to combat sub-freezing temps, but what effect does cold really have? Perhaps I’ll load up a batch of cartridges identical to those in this test, wait for a below-zero day this winter and find out.
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