The Long Range 6mm Creedmoor
Date: Aug 12 2020
The 6.5 Creedmoor (CM), created from a .30 Thompson/Center parent case, was released in 2008. Twelve years later, that cartridge remains an industry obsession. Shortly after its introduction, wildcatters predictably began necking the 6.5 Creedmoor to 6mm; Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI) accepted that version in 2017. The spanking-new round became an instant hit in the high-speed shooting sport of PRS (Precision Rifle Series). It was initially chambered in AR-10 rifles, then chassis rifles, and ultimately, in long-range hunting rifles, like the Browning X-Bolt MAX LR, which was used for testing in this series.
At a glance, the 6mm CM appears to be the ballistic twin of the venerable .243 Winchester, though several factors set them well apart. Largest among these factors is that all current 6mm CM’s that I’m aware of, include rifling twists in the neighborhood of 1:7.5- to 1:7.7, verses a standard 1:10 twist used in .243 Winchesters. This, combined with ample neck length and generous freebore, allows stabilizing long-for-caliber bullets with impressive ballistic coefficients, while also avoiding intruding into powder space. The 6mm Creedmoor also includes a SAAMI maximum pressure of 62,000 psi to the .243’s 60,000 psi, while its 30-degree shoulder lends the cartridge remarkable efficiency – commonly translating into low extreme velocity spreads and minimal brass flow.
Brass is easily formed from popular 6.5 Creedmoor cases via sizing and trimming, though Hornady, Norma, Quality Cartridge, Lapua (small rifle primer pockets) and Starline (large and small rifle primer pockets), just as examples, offer properly headstamped cases. Factory ammunition firebrands such as Hornady, Barnes, Remington, Federal, Winchester, SIG SAUER, Copper Creek and others produce loaded ammunition for sighting and practice, relinquishing once-fired cases for load development.
Lapua brass with small rifle primer pockets were chosen for this test. According to Capstone Precision Group’s (U.S. Lapua distributor) Director of Marketing, Geoff Esterline, after extensive testing, Lapua engineers determined small rifle primers provide an ignition and accuracy advantage over large rifle primers (though, large rifle primers were found to be more reliable in extreme cold or heat). Remington 7½ Benchrest Small Rifle primers were chosen to spark all loads.
While fast 6mm CM rifling twists produce excellent accuracy with bullets down to 75-100 grains, where this cartridge truly distinguishes itself is as a mild-mannered, long-range performer loaded with streamlined, long-for-caliber 105- to 115-grain bullets. Such projectiles flatten long-range trajectory and minimize wind drift, making them naturals for banging steel or toppling varmints “way out there.”
For long-range varmint tasks, especially when the wind stirs, I’ve long lived by a .450 ballistic coefficient (BC) threshold. This is the point at which BC truly begins to make its mark, minimizing bullet drop and wind drift at ranges beyond, say, 500 yards. My long-range tastes involve burrowing rodents, namely across-canyon rockchucks and wind-swept prairie dog towns, arenas where the 6mm CM excels.
Having now dealt with three 6mm Creedmoors – a Ruger Precision Rifle chassis I still have and use; a Savage 10 BA Stealth Evolution chassis rifle tested for another publication; and the excellent Browning big-game targeted rifle used for testing here – it has been my observation that this cartridge becomes fussier as bullet weight increases. Exceptional accuracy can certainly be had with heavier, high-BC bullets, it’s just seems to require more experimenting to find that magic combination. This test rifle was no exception, though some might question my interpretation of acceptable accuracy, as most 6mm Creedmoor loads will print near-MOA groups from any of these quality rifle examples. But when ranges grow extreme, I find nothing less than sub-½-MOA acceptable.
The test rifle was Browning’s exceptional X-Bolt Max LR (Long Range). This handsome rifle includes a composite Max stock with fully adjustable comb and ¼- and ½-inch length of pull (LOP) spacers, vertical “gooseneck” grip and widened forend. The stainless steel barrel is 24-inches long, a heavy sporter with flutes, and includes a fast 1:7.5 twist to accommodate long-for-caliber bullets and 5/8-24 tpi threads with muzzle brake. I removed the brake and added my Rebel Silencers SOS Hunter suppressor. Other nice touches included an extended/oversized bolt handle and dual swivel studs. Its trigger is superbly crisp and broke at around 3 pounds. A Hawke Optics’ Frontier 30 SF (second focal plane) 5-30x 56mm scope was mounted in Warne Mountain Tech rings on a 20 MOA Mountain Tech picatinny rail. This zero-stop turreted scope includes a superfine crosshair Mil Pro reticle and gin-clear optics. It comes with a 3¾-inch sunshade, optional extended throw lever, crosshair illumination and top quality, flip-up metal lens caps. For my tastes, it offers a long range varmint ideal.