IMR-4955’s relative burn rate falls between H-4831 on the fast side and Reloder 22 on the slow end. 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. The highest spread was 113 fps with Speer 145-grain Grand Slams followed by 111 fps with Hornady 162-grain BTSPs.

The lowest extreme spread was 46 fps with Speer 145-grain boat-tail softpoint (BTSP) bullets. That resulted in some rather high extreme velocity spreads. With a seated bullet, IMR-4451 did not completely fill a 7mm Magnum case. Six powders from Alliant and IMR all worked IMR-4451’s burn rate is fairly fast for the 7mm Magnum but is an adequate choice paired with lighter bullets in the cartridge. 300 Winchester Short Magnum and is ideally suited for cartridges that thrive on powders in the midrate burn range. IMR states the powder provides top performance in cartridges that include the. IMR-4451 has a relative burn rate right next to IMR-4350 and Hodgdon H-4350. The addition of nitroglycerine makes the Enduron powders IMR’s first double-base rifle powders. Alliant calls this chemical technology EI technology, and IMR calls it Enduron Technology. 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, the elimination of dinitrotoluene as a deterrent coating and dibutyl phthalate as a stabilizer. Most of these powders worked well with a range of 7mm bullet weights, while one was limited to a single bullet weight. 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.

Handloaders always welcome new powders in their endless effort to improve the velocity and accuracy of their loads. The Browning X-Bolt Speed with a Leupold VX-3i 3.5-10x 40mm scope was used to test loads.

7mm remington rifle