Grumpy old shooters will argue that if the ancient .243 Winchester was loaded to the same pressures as the Creedmoor, and you screwed on a barrel with the same fast twist rates as the Creedmoor, the .243 Winchester would effectively be the same cartridge, but with the sagging shoulders that seem to come with age.
Ballistically, there is not much difference between the two cartridges. An inch or two of barrel length will have more of an impact on velocity than the difference in case capacity. Several pieces of Hornady 6mm Creedmoor brass held an average of 53.25 grains of water while the same number of Federal .243 cases held an average of 54.25 grains of water. The nearly 2 percent difference isn’t enough to sneeze about. A hand loader will see that difference between brands and lots of brass for any cartridge.
So what is the point of the 6mm Creedmoor if it’s really just a shorter, sharper-shouldered .243? There is one primary answer to that question: barrel twist. The Ruger American Predator 6mm Creedmoor, one of the first major factory rifles available for the new 6mm round, was used for hunting and load development for this story. It has a 1:7.7 twist rate. Pouring over catalogs, it was impossible to find anyone chambering the 6mm Creedmoor with anything slower than a 1:8 twist, and some manufacturers were even using 1:7 twist rates or faster to stabilize bullets like the Berger 115-grain VLD Match or Sierra 110-grain MatchKing.
Those twist rates are not common for the .243 or 6mm cartridges that have been kicking around for decades. When the .243 Winchester was introduced in 1955, it was introduced with a 1:10 twist because Winchester rightly assumed that it would become a popular deer rifle with the relatively stubby 100-grain bullets of that era. Those non-very-low-drag bullets needed only a 1:10 twist rate to stabilize them. Remington, which came out with its .244 Remington at about the same time, decided to use a 1:12 twist rate for its new 6mm round. Remington saw its then-new cartridge as primarily a varmint option, mostly shooting bullets of 80 grains or less. That was a big mistake, because the 1:12 twist didn’t stabilize the longer, heavier deer bullets. Remington finally came to its senses, renamed the .244 to the 6mm Remington and switched to the 1:10 twist, but by then the .243 Winchester had already become the 6mm round to use, and the Remington 6mm faded into the sunset. Even the factory .240 Weatherby Magnum only uses a 1:10 twist barrel.
Fast forward 60-plus years, and the shooting industry has changed pretty dramatically. More and more shooters and varmint hunters are interested in long, skinny, high-ballistic coefficient (BC) bullets that buck wind and gravity better at long distance than the stubbier slugs we used – and continue to use – in our aging .24-caliber cartridges.
The industry also learned from the mistakes made with the .244 Remington. Imagine the problems that would have ensued if companies had simply used the standard .243 Winchester or 6mm Remington cartridge and screwed barrels with 1:7 twists on them? Everyone would be promoting the “new” .243 loads with the long 105- and 110-grain bullets for long-range shooting and the owners of older rifles with 1:10 twist barrels would buy (or load) the high-BC bullets for their rifles, which I have done. The result would be bullets going through the target sideways, which I have experienced firsthand. It would have caused no end of nightmares for the industry.
So the solution was a new cartridge and fast-twist barrels. It would also make sense to have the new round function both through AR-style rifles and traditional bolt guns. With the wildly popular 6.5mm Creedmoor already filling that same niche, it was a wise marketing choice to neck down this cartridge for a 6mm version. Many industry insiders have said the 6mm Creedmoor will replace the .243 Winchester over time, just as the .243 replaced the .250 Savage and .257 Roberts rounds, even though it didn’t offer much ballistically over the older .25 calibers.
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After using a 6.5 Grendel to cull a goodly number of Texas feral hogs, I’ve developed a great deal of respect for the cartridge. This has mostly involved nighttime forays shooting with thermal imaging optics. The 2.26-inch confines inherent to AR-15 magazines, and the Grendel’s limited case capacity, make 123- to 130-grain bullets the practical upper limit for such activities. These projectiles chug along at around 2,350/2,450 feet per second (fps), but deliver well out of proportion to its diminutive size.
.240 WEATHERBY MAGNUM
The .240 Weatherby Magnum gets little respect. Knowledgeable varmint hunters will spend a lot of dough to build up a custom 6mm-284 or one of the variations of the 6mm-06 wildcat rounds to get the ballistic features already available in a .240 Weatherby Magnum factory rifle: flat trajectory, good performance in wind and the ability to anchor larger game more reliably if called upon to do so.
The 6mm Creedmoor was designed for long-range target shooting with long and skinny, heavy-for-caliber bullets that slip through the air with the greatest of ease. Wind affects these bullets little; they just fly right through it, almost unaffected.
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