Part 1: A Hunting Rifle for the 21st Century in 6.8 mm Remington SPC

The loads mentioned in this article are safe in my particular rifle, but should not be used without first reducing the load in your rifle, and working up to maximum loads.  Check your loading data against a reliable source before attempting to work up a load.

            Paul Mauser was born in Oberndorf am Neckar, Germany in 1838 to a family of gunsmiths: his father and his four older brothers were all gunsmiths. Arguably, Paul Mauser had the biggest influence on military and hunting rifles used throughout the 20th century.  His first successful design was the Model 1871, which was adopted by the German Empire as the Infanterie-Gewehr 71.  This early design was a conventional looking bolt action chambered in 11 mm using black powder cartridges. The action included only a bolt guide rib as its single locking lug, locking forward of the receiving bridge. The original design was a single shot, but in 1884, the design was updated with an 8-round tubular magazine designed by Alfred von Kropatschek, making it Germany's first repeating rifle. This version was designated the Gewehr 71/84.

Gewehr 71

            Throughout the late 1800s, Mauser continued to improve upon his basic design.  The culmination of Paul Mauser's genius was the development of the Karabiner 98K, which Mauser patented in 1895.  The Karabiner 98 Kurz (often abbreviated Kar98k, K98, or K98k) was a bolt action rifle chambered for the 7.92 x 57 mm Mauser cartridge (often referred to as the 8 mm Mauser) that was adopted as the standard service rifle in 1935 by the German Wehrmacht.

Karabiner 98 Kurz

            In 1903, the United States adopted a new service rifle based on Mauser's model 1898 design, which was designated the M1903 Springfield rifle.  The adoption of the Springfield bolt action was preceded by nearly 30 years of struggle and politics, using lessons learned from the Krag-Jørgensen rifle and contemporary German Gewehr 98 bolt-action rifles. The M1903 not only replaced the various versions of the U.S. Army's Krag, but also the Lee Model 1895 and M1885 Remington-Lee used by the U.S. Navy and the Marine Corps, as well as all remaining single shot trap-door Springfield Models 1873.

M1903 Springfield

         Despite the dramatic changes going on in rifle design at the end of the 19th and the beginning of the 20th century, the vast majority of hunters still used single shot rifles or lever action repeating arms.  The "new fangled" bolt action rifles were military arms, not hunting rifles.  Many hunters felt that using a bolt action rifle with a 5-round magazine was "not needed, was overkill, and simply was not 'fair' to the game being hunted."
 

            This line of thinking seems ridiculous to the vast majority of hunters today, given that the bolt action design has been the basis for most hunting firearm for almost 100 years.  As the dough boys returned from Europe in late-1918 and 1919, the bolt action rifle was familiar and surplus rifles were cheap.  Many hunters either "sporterized" an M1903 by cutting down the stock and took game with it, or stripped the .30-06 barrel off the M1903 action, and used the receiver to build a custom hunting rifle in various calibers of the day. Some of the most popular commercially available bolt action rifles still use the basic Mauser M1898-style action or one that can be directly traced to his innovative design. That Paul Mauser's design is still viable 117 years after his patent was granted speaks volumes of the durability of this advancement.

          Fast forward to 1959, when ArmaLite sold its patent for Eugene Stoner's magnificent AR-15 rifle to Colt.  The U.S. Air Force first adopted the AR-15 in 1962, which ultimately was designated the M16.  Although the development of the M16 was complicated and far from painless, the M16 has been the basis of the main service rifle for the U.S. armed forced for 50 years with no end in sight.  The rifle has gone through several iterations, and forms the backbone of the small arms carried by U.S. Army troops, as well as U.S. Marines and special forces.
 

Several iterations of the basic U.S. service rifle are shown. From top to bottom are the M16A1, M16A2, M4, and M16A4.

            Although the basic design of the M16, or the civilian version AR-15 has been with us for over 50 years, the vast majority of hunters today feel that using a semi-automatic rifle with the potential for a large capacity magazine is "not needed, is overkill, and simply is not 'fair' to the game being hunted."  Does this sound familiar to you?  These arguments against hunting with the AR-15 are as ridiculous today as the arguments against using bolt actions rifles were in 1910.

Some AR-15 manufacturers incorporate the use of a hybrid chamber specification known as the Wylde chamber. Designed by and named after Bill Wylde, this chambering was designed to accurately shoot the military ball ammo of the day while still feeding reliably. Coincidentally, it shoots the longer 80 Gr. bullets commonly used in the sport of Highpower Rifle Competition very well, and is one of the preferred chambers for that use. While the Wylde chamber allows for optimal seating depth of 80 Gr. bullets over .223 Remington and 5.56 NATO, it is capable of accepting both ammunition types. The Wylde chamber is used by most manufacturers who sell "National Match" configuration AR-15 rifle, barrels, and upper receivers.

            There is, however, one valid argument: the .223 Remington (the cartridge for which the AR-15 was designed to shoot) is considered by many sportsman, and most states, to be inadequate for taking deer-sized game.  Many states require a bullet of at least 6 mm (0.243 inches) and a magazine capacity of no more than 5-rounds for hunting deer.  Louisiana does allow the use of .22 caliber center-fire rifles and has no regulations related to magazine capacity when hunting deer. The basic AR-15 in .223 Remington is legal for taking deer in our state, although many of the rifles sold to sportsman are really not configured as hunting rifles.

.223 Remington Loads Developed for Hunting Predators, Hogs, and Deer  Bullet Powder Charge Weight (Gr) Muzzle Velocity (FPS) Use Velocity at 300 yds (FPS) Energy at 300 yds (ft-lbs) 55 Gr Hornady SP Varget 26.4 3109 ± 18 Predators 1975 476 IMR8208 XBR 25.8 3165 ± 20 Predators 2017 497 A2495 26.2 3199 ± 14 Predators 2043 510 IMR4320 26.1 3057 ± 15 Predators 1935 457 60 Gr Nosler Partition RL-15 25.5 2926 ± 37 Hogs, Deer 1808 435 70 Gr Barnes TSX BT RL-15 24.5 2895 ± 6 Hogs, Deer 2058 564 All loads with Wolf NCSRM primers

            A couple of years ago, I removed a barrel from my competition service rifle after firing approximately 4000 rounds through it. For competition purposes, where we shoot at a 6-inch X-ring at 600 yards, the barrel was "shot out."  But, the barrel was still way more accurate than most hunting barrels for reasonable ranges out to 300 yards.  The stainless steel Krieger barrel has a .233 Remington Wylde chamber (see sidebar at right for an explanation) and a 1 in 7.7" twist, which are ideal for shooting the long 80-82 Gr. competition bullets. I took this competition barrel and asked Bob Jenkins to turn down the outside dimension of the barrel to reduce its overall weight, following which, I built a nice little predator hunting rifle using a flat-top Rock River Arms upper receiver. The barrel likes both the 60 Gr. Nosler Partition bullet, and the 70 Gr. Barnes TSX BT bullet (Barnes recommends a 1 in 8" or faster twist barrel for this bullet.) If you are considering a hunting rifle in .223 Remington and think you may hunt both predators, hogs, and deer with it, I urge you to get a rifle length barrel (as opposed to a carbine length barrel) with a 1 in 8" twist.  This will allow you to shoot the more appropriate hunting bullets available in .224 caliber that are extremely lethal for coyotes, hogs, and deer alike.

The author with a very nice bobcat taken in February 2012 in Catahoula Parish using an AR-15 in .223 Remington.

            Even though I had built the hunting rifle in .223 Remington, I still felt somewhat under-gunned for deer.  Although very much in its infancy, designers have been working on new, more powerful cartridges for the basic AR-15 design.  After careful consideration of the currently available cartridges, I settled on building a new deer hunting rifle in 6.8 mm Remington SPC (Special Purpose Cartridge).  This cartridge, which is based upon the .30 Remington, was developed by Remington Arms with collaboration from individual members of the U.S. Army Marksmanship Unit, U.S. Special Operations Command to possibly replace the 5.56 NATO cartridge in a Short Barreled Rifle (SBR)/Carbine.  The 6.8 SPC was designed to address the deficiencies of the terminal performance of the 5.56 NATO cartridge currently in service with the U.S. Armed Forces.

 

            The 6.8 mm Remington uses bullets of 0.277 inches, which is the same caliber as the venerable .270 Winchester, although the ballistics of the two cartridges are wildly different.  The .270 Winchester was developed by necking down the .30-06 Springfield to 0.277 inches, with SAAMI specifications for an overall length of 3.340" and a case capacity of 67 Gr. of water.  The 6.8 mm Remington, on the other hand, was developed from the .30 Remington case, has an overall length of 2.315" (see discussion on magazines below) and a case capacity of 37 Gr. of water (45% less case capacity). Although the performance of the 6.8 mm Remington is limited by the length of the AR-15 magazine, the cartridge is still a solid performer for deer size game out to about 200-300 yards, depending on bullet selection. Given the need for a relatively short-for-caliber overall length, lighter bullets yield the best performance in the AR-15 platform. For deer and hogs, bullets in the 95-115 Gr. weight range give the best combination of velocity and terminal performance. Assuming that bullets require a velocity of 1800 fps to perform on game, the 95 Gr. Barnes TTSX has enough velocity out to about 350 yards, and the Sierra 110 Gr. GameKing has enough velocity out to about 250 yards to expand and quickly kill game.  In comparison, the .270 Winchester is still chugging along well about 1800 fps out at 500 yards.

            The choice of a magazine for the 6.8 mm Remington actually turns out to be more important than one might otherwise assume.  Given that the 6.8 mm Remington was designed to shoot in rifles that were developed around the .223 Remington, the overall length must conform to the length of the .223 Remington magazine.  Overall length for the .223 Remington is set at 2.26". Manufactures have developed magazines for the 6.8 mm Remington with this same overall length in mind.  However, one manufacturers of 6.8 mm Remington magazines, Precision Reflex, Inc, makes magazines that will fit into any AR-15 lower receiver, but allows an overall length of 2.315".

6.8 mm Rem, 95 Gr , 2800 fps 6.8 mm Rem, 110 Gr , 2530 fps .270 Win, 130 Gr, 2912 fps Range (Yds) Velocity (fps) Energy (ft-lbs) Trajectory (Inches) Velocity (fps) Energy (ft-lbs) Trajectory (Inches) Velocity (fps) Energy (ft-lbs) Trajectory (Inches) 0 2800 1654 -1.5 2530 1563 -1.5 2912 2448 -1.5 50 2641 1471 -0.13 2391 1396 0.01 2797 2258 -0.19 100 2487 1305 0 2256 1243 0 2685 2080 0 150 2339 1154 -1.28 2125 1103 -1.72 2575 1914 -1.01 200 2196 1017 -4.15 1999 976 -5.37 2468 1759 -3.33 250 2058 893 -8.83 1877 861 -11.19 2364 1613 -7.08 300 1925 781 -15.56 1761 757 -19.49 2263 1478 -12.39 350 1798 682 -24.64 1650 665 -30.59 2163 1351 -19.39 400 1676 593 -36.41 1545 583 -44.88 2067 1233 -28.25 450 1562 515 -51.28 1446 511 -62.83 1973 1123 -39.15 500 1455 447 -69.72 1356 449 -84.93 1881 1022 -52.28

            When building my rifle, I had several requirements. I wanted a rifle-length gas system (as opposed to a carbine- or M4-length gas system), a 1 in 11" twist stainless steel barrel with an 6.8 SPC II chamber, an aftermarket single-stage trigger, and walnut furniture.  The barrel actually turned out to be the most difficult item to find, as the vast majority of barrels on the market in 6.8 Remington SPC are fast twist (for using heavier bullets) with M4-length gas systems.  Since the cartridge was designed for the M4 platform, the additional length of the rifle-length barrel over an M4-length barrel gives very little additional performance (estimated at about 25 additional fps per inch of additional barrel).
 

The SPC II designation refers to the updated chamber specification for the 6.8 SPC. The freebore in the chamber was increased by 0.1", which reduced the chamber pressure of the 6.8 SPC and allowed higher power ammunition to be used safely. With the new chamber specification, the 6.8 SPC is able to realize its full potential as a hunting/combat round. Other updated chamber specs exist, including the 6.8 x 43 mm and Noveske 6.8mm SPC MOD 1, which are similar to the SPC II.

            I found my barrel at Bison Armory, and it was exactly what I desired.  The 20" stainless steel barrel had the 6.8 SPC II chamber, a 1 in 11" twist, M4 feed ramp cuts (not needed for my purposes, but nice to have), button rifling, and was threaded for a muzzle brake.  The barrel is fluted under the hand guard to reduce weight and increase cooling capacity, and was finished with a black Cerakote finish.

           For the gas system, I chose to use a Low Pro gas block produced by Yankee Hill Manufacturing (YHM).  Low profile gas blocks are extremely simple devices. They are intentionally minimized for weight and to fit under a free float forearm. The gas block was attached via two set screws and could have been pinned to the barrel as an option, for instance, if I ever planned to take the rifle into a combat situation (I do not!).  The rifle-length gas system can be problematic, and this is something to consider when choosing your barrel.  This gas length can exhibit short stroking when used with light bullets (85 and 90 Gr.) in conjunction with very fast powders. Cycling is fine with 110 Gr. and heavier bullets.  Through my limited testing to date, I have fired 10 different loads with the 95 Gr. Barnes TTSX bullet, and 5 different loads with the 110 Gr. Sierra GameKing bullet with no malfunctions at all.

            There are a number of high quality aftermarket triggers for the AR-15, from 2-stage match triggers to single stage hunting triggers.  For this rifle, I chose the Timney Triggers single stage competition trigger. The trigger is factory preset with a pull weight of 3 pounds.  Installation was quick and no adjustments were necessary. It was a true drop-in trigger. The trigger module installed using my rifle's original hammer and trigger pins and the proprietary design eliminates pin rotation and walkout.
 

            The beautiful walnut furniture clearly fell into the "I want" category and not into the "I need" category.  In fact, I surely increased the weight (10.7 pounds overall weight) and lost the benefits of a free floated hand guard by choosing to go with walnut.  But, dang, it looks so good!

            I topped the Rock River Arms (RRA) flattop upper receiver with a high profile RRA scope mount, which by the way looks like it could stand recoil from a .500 Nitro Express, and a Leupold Rifleman 3-9X40 mm scope with a "Rifleman Ballistic Reticle."  The ballistic reticle is nothing more than additional aiming dots underneath the crosshair, which allows the shooter to develop additional aiming points for longer shots.  I have not shot the new rifle enough to know how those aiming dots will be used.

6.8 mm Remington Loads Developed for Hunting Hogs and Deer  Bullet Powder Charge Weight (Gr) Muzzle Velocity (FPS) Group Size (in) No. Shots in Group 95 Gr Barnes TTSX RL-10X 28.5 2693 ± 22 2.65 5 A2230 31.0 2831 ± 13 3.24 5 H322 29.5 2745 ± 5 3.14 5 H322 30.0 2805 ± 23 2.79 5 A2200 28.6 NR 2.1 5 A2200 30.5 NR 5.54 5 RL-7 26.0 NR 1.03 3 IMR4198 25.3 NR 2.72 5 X-Terminator 30.0 NR 3.26 5 X-Terminator 31.0 2811 ± 8 1.35 5 110 Gr Sierra GameKing H335 29.5 2530 ± 16 0.97 8 H322 29.0 2600 ± 18 3.1 10 A2200 28.6 2654 ± 15 0.97 8 X-Terminator 30.0 2627 ± 15 1.22 5 RL-10X 26.5 2362 ± 11 2.47 10 NR = Not Recorded | All loads used Hornady brass and Remington 7½ primers

            With only 100 rounds downrange out of the rifle I have made two observations of note: (1) my rifle hates (so far) the 95 Gr. Barnes TTSX bullet and (2) my rifle loves the 110 Gr. Sierra GameKing bullet.  The Barnes Tipped TSX features a lead-free 100% copper body with multiple rings circumferential cuts into the shank.   Because the bullet is lead-free, it is long for its weight, which increases bearing surface.  Dan Zelenka has used this bullet in his recently built 6.8 mm Remington carbine with excellent results, so it is not clear why my rifle will not shoot the bullet very well.  The best group that I was able to generate was slightly over 1", but was only a 3-shot group.  The Sierra GameKing, on the other hand, is a standard soft-point flat-base spitzer with an exposed lead nose.  The bullet turned in some fine groups, including two loads that grouped under an inch.