<p><strong>Handloaders always welcome new powders in their endless effort to improve the velocity and accuracy of their loads. So in anticipation of stepping up the performance of my 7mm Remington Magnum, new powders have been tested, including Alliant Reloder 17, 23 and 33; and IMR-4451, -4955 and -7977. Most of these powders worked well with a range of 7mm bullet weights, while one was limited to a single weight bullet.</strong></p>

- John Haviland

Several of the powders contain features such as the ability to maintain consistent velocities over a wide variation in temperatures, an additive that reduces buildup of copper fouling in the bore and the elimination of dinitrotoluene as a deterrent coating and dibutyl phthalate as a stabilizer. Alliant calls this chemical technology EI technology, and IMR calls it Enduron Technology.

IMR POWDERS 

The addition of nitroglycerine makes the Enduron powders IMR’s first double-based rifle powders. IMR4451 has a relative burn rate right next to IMR-4350 and Hodgdon H-4350. IMR states the powder provides top performance in cartridges that include the .3006 and .300 Winchester Short Magnum and is ideally suited for cartridges that thrive on powders in the midrate burn range. IMR-4451’s burn rate is fairly fast for the 7mm Magnum but is an adequate choice paired with lighter bullets in the cartridge.

With a seated bullet, IMR-4451 does not completely fill a 7mm Magnum case. That resulted in some rather high extreme velocity spreads. The lowest extreme spread was 46 fps with Speer 145-grain boat-tail soft point (BTSP) bullets. The highest spread was 113 fps with Speer 145-grain Grand Slams followed by 111 fps with Hornady 162-grain BTSPs. However, group sizes were not all that much different than other powders shot in a Browning X-Bolt Speed rifle, which was used to shoot all the loads listed in the accompanying table.

IMR-4955’s relative burn rate falls between H-4831 on the fast side and Reloder 22 on the slow

このストーリーは、Handloader の June - July 2017 版からのものです。

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