Revisiting the 6mm Creedmoor
Date: Feb 15 2022
The 6mm Creedmoor is nothing more than the hugely popular 6.5 Creedmoor necked to 6mm. The 6.5 Creedmoor launched in 2008, itself created from a .30 Thompson/Center (T/C) parent case. It took a few years for the 6.5 Creedmoor to truly catch on, and until 2016 or so, for someone – John Snow actually – to neck the case down to 6mm. The cartridge was given the thumbs-up by the Sporting Arms and Ammunition Manufacturers’ Institute in 2017. Initially chambered in AR-10 rifles, when the high-speed shooting sport of PRS (Precision Rifle Series) was in its infancy, it has become more common to see the cartridge offered in long-range hunting rifles, and especially chassis rifles like the Ruger Precision Rifle used here for testing. Ruger was one of the first major riflemakers to adopt the cartridge.
Firearms curmudgeons who hate everything new, immediately labeled the 6mm Creedmoor a .243 Winchester knockoff. Dimensionally, that is somewhat true, though the Creedmoor was released in rifles universally including 1:7.5- to 1:7.7-inch rifling twists, while standard .243 Winchesters usually include 1:10 rifling twist. Creedmoors were also given a longer neck length and additional freebore to better handle long-for-caliber bullets without intruding into powder space. The 6mm Creedmoor includes a Maximum Average Pressure (MAP) rating of 62,000 psi to the .243’s 60,000 psi. One could add the Creedmoor’s modern 30-degree shoulder angle, which seems to lend the cartridge more efficiency. In any case, the 6mm Creedmoor usually shows a 100 feet per second (fps) velocity advantage over the older .243 Winchester, despite slightly less powder capacity.
Today, ready-made 6mm CM cases can be purchased from Hornady, Norma, Quality Cartridge, Lapua (small rifle primer pockets) and Starline (large and small rifle primer pockets), and factory ammunition is available from Hornady, Barnes, Remington, Federal, Winchester, SIG Sauer, Copper Creek and others – all including proper headstamps. I’ve no doubt forgotten someone.
In the beginning, I loaded Hornady Large Rifle primer brass, but have since come to prefer Lapua Small Rifle primer brass. The guys at Capstone Precision Group tell me Lapua engineers, after extensive testing, determined small rifle primers provided an accuracy edge. Be it the primer size, or Lapua quality, my groups shrank ever so slightly after adopting the Finnish cases. I’ve also come to prefer Federal Premium Gold Medal Match primers – GM205M – for this cartridge.
Ruger’s Precision Rifle was on the leading edge of the chassis revolution. The 11 pound Precision includes a folding MSR stock with adjustable length of pull – 12 to 15.5 inches – and comb height. The cold hammer forged, chrome-moly barrel is 26 inches long, includes 5R rifling and holds 5/8-24 threads fitted with Ruger’s Hybrid Muzzle Brake that reduces recoil while minimizing noise and muzzle blast. The barrel includes 1:7.7 rifling twist and measures .75 inch at the muzzle. The Ruger Marksman Adjustable trigger is externally adjustable from 2.25 to 5 pounds and the adjustment wrench is stored in the bolt shroud. The barrel is completely free-floated and protected by a 15-inch aluminum handguard with Magpul M-LOK slots on all four sides. A 20 MOA Picatinny rail secured with #8-40 screws is included. The "upper" receiver and one-piece bolt are precision CNC-machined from pre-hardened 4140 chrome-moly steel, the “lower” magazine-well halves machined from 7075-T6 aluminum and Type III hard-coat anodized. A three-lug, nitride-coated bolt provides a 70-degree throw via an oversized bolt handle, the dual cocking cams and full body bolt body provided smooth cycling. The rifle includes an AR-style pistol grip and safety switch and rounds are fed from a 10-round Magpul PMAG magazine. The test rifle was equipped with a Hawke Optics’ Frontier 30 SF (second focal plane) 5-30x 56mm scope set in high rings. This zero-stop turreted scope includes a super-fine Mil Pro reticle and clear optics. It comes with a 3¾-inch sunshade, optional extended throw lever, crosshair illumination and top-quality, flip-up metal lens caps.
I wanted to test newer powders this go-round, curious to see if improved temperature stability and cleaner-burning formulas would improve results. I also updated the bullet lineup to include some big-game numbers as well as modern target/varmint options. The 88-grain Hammer Bullets Hammer Hunter, a monolithic copper slug that is long for weight (a minimum 1:8 twist is recommended for proper stabilization). It includes an estimated G1 ballistic coefficient (BC) of .472 and would make an excellent pronghorn or deer bullet. The lighter weight should generate some velocity when paired with the three IMR Enduron powders – IMR-4166, IMR-4451 and IMR-4855. Another relative lightweight, the 95-grain Sierra Tipped MatchKing (TMK) is a favorite varmint option from my fast-twist 6mm Remington, combining excellent velocities with a wind-bucking .500 G1 BC. I wouldn’t hesitate to shoot deer or hogs with this bullet. The TMK was paired with Hodgdon H-4350 and Superformance and Winchester StaBALL 6.5 (distributed by Hodgdon).
Sitting in the middle is the 103-grain Hornady ELD-X, a bullet I’ve used on game as varied as coyotes, wild hogs and white-tailed deer. It’s a reliable stopper and includes a .512 G1 BC for long-range work. The ELD-X was paired with the newest from Alliant; Reloder 16, 23 and 26. The 105-grain Nosler RDF (Reduced Drag Factor) includes a spear-like ogive and elongated boat-tail to produce a phenomenal .571 G1 BC. The jury is out on whether these target bullets will expand on smaller varmints, but they will certainly bang steel gongs way out there. Shooters World was paired with this bullet, sampling Precision Rifle, Long Rifle and SW-4350. Finally, we have the 108-grain Berger Elite Hunter. It offers a .559 G1 BC in a big-game bullet reliable enough for any caribou- or black bear-sized animal. Vihtavuori powders served here, including the new N-555, proven N-560 and even newer N-565.