.375 Remington Ultra Magnum (using Hornady bullets)
Date: Aug 14 2014
In 1998 Remington introduced the .300 Remington Ultra Mag on a belt-less case inspired by the .404 Jeffery, and began building a "family" of cartridges based on this case, with the .375 RUM introduced in the fall of 2000. Advertised velocities listed a 270-grain bullet at 2,900 fps and the 300-grain Swift A-Frame at 2,760 fps. In testing early production ammunition, both loads easily exceeded those figures from a Model 700 BDL with a 26-inch barrel, which recorded 2,979 and 2,799 fps, respectively.
The .375 RUM is an impressive "medium bore" big game cartridge that offers notably flatter trajectory than the .375 H&H Magnum, but at the cost of greater recoil. Remington currently does not catalog rifles for this cartridge.
Large rifle magnum primers are strongly suggested to achieve correct powder ignition with the Remington 9 ½ Magnum being used to develop the accompanying data. A Federal 215 Large Rifle Magnum primer can be substituted.
It is strongly suggested to avoid reducing "starting" powder charges, or hang-fires and erratic pressures can occur.
To duplicate factory load performance using 300-grain bullets, IMR-4350, IMR-4831, Hodgdon H-4350, H-4831 and Alliant Reloder 19 proved top choices and each produced notable accuracy.
A roll crimp is suggested to help keep bullets in place when cartridges (in the magazine) are subjected to recoil and will also keep bullets from being deep-seated when rounds are chambered robustly in the field.