Handloads: .300 Winchester Magnum

posted on April 28, 2021

.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.


Bergara Premier Mglite Rifle
Bergara Premier Mglite Rifle

New For 2022: Bergara Premier MgLite Rifle

New for 2022, Bergara introduces its new Premier Series MgLite rifle, combining carbon fiber and magnesium construction for an ultra-lightweight, long-range bolt action.

New For 2022: Stoeger STR-9C Optic Ready

New for 2022, Stoeger introduces a new addition to its compact STR-9C handgun line with an optic read model, the STR-9C Optic Ready.

New For 2022: Browning X-Bolt Speed Ovix Suppressor Ready

Browning introduces a new addition to the X-bolt Speed series for 2022 with a suppressor ready model with pre-threaded barrel.

New For 2022: Kelbly's Inc. Nanook MG Rifle

New for 2022, Kelby's Inc. unveils its ultra-lightwight Nano MG precision rifle, offered in three different calibers.

First Look: Walther PDP Color Options

Building off the success of its PDP handguns, Walther Arms now offers three additional color options for the frames of the PDP line.

New For 2022: Black Collar Arms MBA

New for 2022, Black Collar Arms releases it Modern Bolt Action, or MBA, straight-pull, bolt-action rifle which uses commonly available AR-10 parts in its construction.


Get the best of American Rifleman delivered to your inbox.