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

Ruger Acquires
Ruger Acquires

Ruger Buys Anderson Manufacturing

Ruger announced on July 1 it has acquired all assets of Anderson Manufacturing, a recent top 10 producer of firearms in the U.S.

Favorite Firearms: Anticipating Answers

Everyone has a favorite gun, but not many have a story quite like the one from NRA member Jim Schollhammer.

Rifleman Report: Safe Passage

While the phrase “tools of the trade” may refer to specific items that a worker uses to ply his or her vocation, it could just as easily be a reference to the firearms, knives and other everyday carry, or EDC, gear that the average citizen uses to ensure his or her safe passage through the course of an uncertain, sometimes dangerous, daily existence.

I Have This Old Gun: Star Model 1914 Auto Pistol

The Spanish/Basque city of Eibar is one of Europe’s great arms-manufacturing centers, with a history in gunmaking dating back to the 1500s.

The Armed Citizen® July 28, 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.

"Clay Pigeons That Shoot Back:" Aerial Gunnery Training & Combat In WWII

"Even though slated early in my training period to be a photographer, I had to go through the "firing mill" as intensively as the others. For months, we burned up so much powder, I began to be afraid there wouldn't be enough for the boys who were really slugging it out at high altitudes ..."

Interests



Get the best of American Rifleman delivered to your inbox.