Handloads: .300 Winchester Magnum

posted on April 28, 2021
** When you buy products through the links on our site, we may earn a commission that supports NRA's mission to protect, preserve and defend the Second Amendment. **
hand300.jpg

.300 Winchester Magnum specsThe folks at Cooper Firearms of Montana commonly shoot Barnes Triple Shock X (TSX) and Tipped Triple Shock X (TTSX) bullets to test the accuracy of their rifles. That’s a good recommendation for a bullet, as Cooper guarantees its rifles to shoot 1/2-minute-of-angle groups at 100 yds.

I’ve been shooting a Cooper Open Country Long Range rifle chambered in .300 Win. Mag. loaded with Barnes 165-gr. TTSX bullets, and am pleased with the accuracy. The target included with the Open Country rifle noted that the Barnes bullet was handloaded with Ramshot Magnum. Magnum has provided good accuracy for me in several other .300 magnums. This trend continued with the Open Country, shooting five, three-shot groups that ranged from 0.31" to 0.95" and averaged 0.63", with a standard deviation of velocity of 16 f.p.s. throughout 12 shots. The Barnes Reloading Manual Number Four specifies two additional grains of Magnum than is listed in the recipe as the maximum propellant charge for the TTSX bullet, so velocity could be increased somewhat beyond the 3046 f.p.s. that the Open Country had produced. The load’s great accuracy, though, presented a good place to stop load development.

Notice that the cartridge overall length of 3.520" is longer than the .300 Win. Mag.’s established maximum of 3.340". That extra length still positioned Barnes bullets well short of contacting the start of the rifling in the Open Country—a critical point to check for each specific rifle. To remove the chance such a jump might be detrimental to accuracy, cartridges were gauged on a Hornady Lock-N-Load Concentricity Tool to ensure the bullets were seated straight in the cases so that, upon firing, they squarely contacted the rifling and made a beeline to the target.

Latest

Weatherby 307 New Models F
Weatherby 307 New Models F

New For 2025: Weatherby Model 307 Range XP 2.0 & Alpine ST Rifles

Weatherby's Model 307 bolt-action rifle opens up a world of aftermarket components to consumers, thanks to its Model 700 receiver footprint, and the company now has two new models for hunters and sport shooters.

Preview: Thunderbolt To The Rebels | The United States Sharpshooters In The Civil War

Author Darin Wipperman provides a tantalizing glimpse into the world of Berdan’s sharpshooters during the American Civil War.

Gun Of The Week: Rock River Arms LAR-22 Tactical Carbine

This week, we're on the range with the Rock River Arms LAR-22 Tactical Carbine, a rimfire variant of the AR-15 that's designed for reliability and gives enthusiasts a way to shoot affordably.

The Armed Citizen® July 11, 2025

Read today's "The Armed Citizen" entry for real stories of law-abiding citizens, past and present, who used their firearms to save lives.

Japanese Last-Ditch Small Arms Of World War II

The crude assortment of fighting tools used by the Japanese during World War II give clues of an unprepared and unmatched last-ditch fight that ultimately lead to Allied victory.

Federal Ammunition Awards 2025 Tom Knapp Memorial Scholarships

Federal Ammunition recently awarded the 2025 Tom Knapp Memorial Scholarships to two 4-H shooting sports teen ambassadors.

Interests



Get the best of American Rifleman delivered to your inbox.