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Shooting: 6MM Rifle Cartridges Remain Worthy in the Field

Two recent 6 mm rifle cartridges build on the dual-purpose versatility of their predecessors.

Shooting: 6MM Rifle Cartridges Remain Worthy in the Field

The metric equivalent of .243 inch is 6.172 mm, but Remington rounded down when in 1963 it named the 6 mm Rem. cartridge. (Photo by Adam Heggenstaller)

Although .30-caliber cartridges are perennial favorites and 6.5 mm rounds now get a lot of attention, cartridges that fire 6 mm bullets are ideal for many American hunters. They offer low recoil and flat trajectories for varmint and predator hunting, and they have enough punch for deer-sized game.

This dual suitability has been a defining characteristic of 6 mm rifle cartridges, and they can even be effective on larger game if partitioned, bonded or mono-metal bullets are used. (In 2014 my wife used a .243 Win. to take a gemsbok and wildebeest in Africa with one well-placed shot each.)

Let’s look at the progress of 6 mm rifle cartridges, which continues today for good reason.

In 1955 Remington introduced the .244 Rem. cartridge. It was based on the .257 Roberts, which was a .25-caliber cartridge derived from the 7x57 mm Mauser.

The .244 Rem. utilized a bullet with a diameter of .243 inch, which equates to 6.172 mm, and had a land-to-land bore diameter of .237 inch. Suitable for varmints with lightweight 75-grain bullets and deer-sized game with 90-grain bullets, the .244 Rem. would become one of the first commercially successful 6 mm cartridges in America.

But Remington made a mistake with the .244. Originally, the company specified a rifling twist rate of one turn in 12 inches. This limited the cartridge’s ability to stabilize longer, heavier bullets. In 1963 Remington renamed the .244 Rem. the 6 mm Rem. and introduced it in the new Model 700 bolt-action rifle with a 1-in-9-inch twist rate.

6MM Rifle Cartridges
With 85- to 100-grain bullets, the .243 Win. is an excellent whitetail cartridge. Lighter bullets make it suitable for predators. (Photo by Richard Mann)

However, it was too late. Also in 1955, Winchester had introduced the ballistically similar .243 Win. It was based on the .308 Win. case and used the same diameter bullet as the .244 Rem. But Winchester was smarter with its introduction; the company chose a 1-in-10 twist rate that would stabilize heavier bullets.

The .243 Win. quickly became a favorite of hunters who wanted one rifle they could use for groundhogs, rock chucks, coyotes, and deer- or pronghorn-sized big game. It became known as a both-ways (varmint/big-game) cartridge. Shortly after its introduction, the .243 Win. earned a spot in the top 10 best-selling rifle cartridges and has remained there ever since. The first deer rifle my father ever purchased was a .243 Win., and I watched him use it with great success on groundhogs and deer for more than 40 years.

Weatherby recognized the popularity of the .243 and in 1968 introduced the .240 Wby. Mag. It was the last cartridge designed by Roy Weatherby and could push a 60-grain bullet to 3,800 fps and a 100-grain bullet to 3,300 fps. It had a velocity advantage over the 6 mm Rem. and the .243 Win., and it filled the same niche. The .240 Wby. Mag. is still with us—Weatherby offers factory ammo and rifles for it—but like many Weatherby cartridges, it never achieved mass appeal.

6MM Rifle Cartridges
Data represents the flattest-shooting big-game factory loads for each cartridge, using factory-advertised velocities and ballistic coefficients. Data was calculated at sea level with a temperature of 59 degrees, barometric pressure of 29.92 inHg and 50 percent relative humidity. Bullet weight measured in grains. Velocities measured in fps. Bullet drops based on a 100-yard zero.

In 2003 Winchester introduced another 6 mm called the .243 WSSM (Winchester Super Short Magnum). It had a shorter overall length than any previous 
6 mm—the same as the .223 Rem.—but was much fatter. The base of the .243 WSSM cartridge measured .555 inch in diameter as compared to .471 inch for the .243 Win. Essentially a ballistic twin to the .243 Win., it enjoyed an initial flurry of fanfare and storm of popularity. However, the .243 WSSM faded away just as quickly as it arrived. It could not dethrone Winchester’s older 6 mm.

Though it had been a wildcat cartridge since 2009, Hornady legitimized the 6 mm Creedmoor in 2017. It’s essentially a 6.5 Creedmoor necked down to 6 mm. With a specified twist rate of 1 turn in 7.5 inches and a case slightly shorter than the .243 Win., the 6 mm Creedmoor can utilize longer, sleeker bullets and still work in short-action rifles.

6MM Rifle Cartridges
The defining traits of the 6 mm ARC are its ability to function in the AR-15 and its use of bullets with high ballistic coefficients. (Photo by Richard Mann)

The 6 mm Creedmoor and .243 Win. are very close in ballistic performance. However, the 6 mm Creedmoor’s compatibility with bullets having high ballistic coefficients allows it to perform better at extreme distances. For shooting game at typical ranges, the 6 mm Creedmoor offers no practical advantage over the .243 Win.

6MM Rifle Cartridges
More than six decades of cartridge development separate the venerable .243 Win. (left) from the recently introduced 6 mm Creedmoor (center) and 6 mm ARC. (Photo by Richard Mann)

On the other hand, the new 6 mm ARC (Advanced Rifle Cartridge) does. The 6 mm ARC is based on the 6.5 Grendel (which has the 7.62x39 mm as its parent). Because of its shorter overall length, the 6 mm ARC works well in the AR-15 platform—something no previous 6 mm cartridge could do. Like with the 6 mm Creedmoor, the fast 1-in-7.5 twist rate of the 6 mm ARC also permits the use of bullets with high ballistic coefficients.

This gives hunters who like the varmint/big-game capability that 6 mm cartridges offer the option to use an AR-15. (The AR-15 platform can be made to work with the .243 WSSM, but the configuration never became commercially viable.)


If you want to hunt with an AR-15, the 6 mm ARC is the way to go. It might be the best dual-purpose varmint/deer cartridge yet for that platform. If you want to ring steel out past 500 yards, as well as hunt deer and vermin at more sensible distances, the 6 mm Creedmoor will do both jobs admirably. The 6 mm Rem. and .243 WSSM are dead, and the .240 Wby. Mag. never gained a huge following. If you own rifles for any of these, don’t fret. They’re all excellent; you will just likely struggle to find factory ammo.

The .243 Win. is still the king of 6 mm cartridges. I’ve effectively used it across the United States and in Africa. It’s not the fastest or flattest-shooting 6 mm, and it’s not AR compatible. But it has been proven and offers a great balance of everything that makes a 6 mm rifle cartridge worth considering in the first place.

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