6.8 mm Remington SPC

The 6.8 mm Remington Special Purpose Cartridge (aka 6.8 SPC, 6.8 SPC II & 6.8×43mm) is a rifle cartridge that was developed by Remington Arms in collaboration with members of the U.S. Army Marksmanship Unit, United States Special Operations Command to possibly replace the 5.56 NATO cartridge in a Short Barreled Rifle(SBR)/Carbine.

Based upon the .30 Remington cartridge, it is midway between the 5.56×45mm NATO and 7.62×51mm NATO in bore diameter and muzzle energy. It uses a 0.277 in (7.0358 mm) diameter bullet, the same as that used in the venerable .270 Winchester hunting cartridge. It is particularly adaptable to current 5.56 mm NATO firearms, sharing the same cartridge overall length of 2.260 in.

Development
The 6.8mm SPC cartridge was designed to address the deficiencies of the terminal performance of the 5.56x45mm NATO cartridge currently in service with the U.S. Armed Forces. The cartridge was the result of the Enhanced Rifle Cartridge program. Participating in the program were U.S. Special Operations soldiers, as well as armorers and other technicians from the United States Army Marksmanship Unit. The goal was to create a cartridge that would bridge the gap between 5.56mm and 7.62x51mm NATO.

The program started the design by using a .30 Remington case, which was modified in length to fit into magazines that would be accommodated by the magazine wells of the M16 family of rifles and carbines that are currently in service with the U.S. Armed Forces.

In tests, it was determined that a 6.5mm barrel had the best accuracy, but a 7mm barrel had the best terminal performance. Further tests showed that a 6.8mm barrel was the best compromise between the two, providing accuracy, reliability and terminal performance up to 500 meters. The combination of the cartridge case, powder load, and projectile easily outperformed the 7.62x39mm Soviet cartridge, with the new cartridge proving to be about 200 ft/s faster. The resulting cartridge was named the 6.8 Remington Special Purpose Cartridge due to the size of its barrels and the fact that it was based on the .30 Remington case.

In general, adapting an AR-style rifle to the new cartridge only requires the replacement of the barrel, bolt and magazine of the 5.56mm-chambered rifle; but to further streamline and simplify the conversion process many parts manufacturers sell complete upper receiver assemblies chambered for 6.8 SPC alongside their conversion kits focusing on the key individual parts. While a complete 6.8 SPC assembly is a somewhat more expensive route, the conversion of an existing 5.56mm/.223 rifle to 6.8 SPC using a complete upper assembly takes less than a minute on an AR platform rifle without the need for specialized tools or skill. In contrast, when swapping out the individual component parts, a significant level of gun smithing experience, special tools, and time are generally required to detach the barrel from the rifle's upper receiver and the gas system, and conversely those same needs are required for the reassembly of the upper receiver with the new 6.8 SPC barrel. Also, there is the issue of having to readjust the sights if a new barrel is placed on an existing upper receiver.

The 6.8 mm Remington SPC was designed to perform better in short barreled CQB rifles after diminished performance from the 5.56 NATO when the AR15 was changed from the rifle configuration to the current M4 carbine. The 6.8 SPC delivers 44% more energy than the 5.56 mm NATO (M4 configuration) at 100 - 300 m. The 6.8mm SPC is not the ballistic equal of the 7.62x51mm NATO cartridge, however; it has less recoil, is more controllable in rapid fire, and lighter, allowing operators to carry more ammunition than would otherwise be possible with the larger caliber round. The 6.8 mm generates around 1759 ftlbf of muzzle energy with a 115 gr bullet. In comparison, the 5.56x45mm round (which the 6.8 is designed to replace) generates around 1325 ftlbf with a 62 gr bullet, giving the 6.8mm a terminal ballistic advantage over the 5.56mm of 434 ftlbf. One of the enigmatic features of this cartridge is it being designed for a short barrel carbine length rifle that the standard rifle length is (usually 16 in). The round only gains about 25 - 35 ft/s for every 25 mm of barrel length past the standard 16 in barrel (all else being equal) up to barrel's length around 22 - 24 in with no gain/loss in accuracy. It also does very well in rifles with less than 16 in barrels. In recent developments (the period 2008-2012) the performance of the 6.8 SPC has been increased by approximately 200 to 300 ft/s by the work of one ammunition manufacturer Silver State Armory LLC (SSA) and a few custom rifle builders using/designing the correct chamber and barrel specifications. Also, more recently, LWRC, Magpul & Alliant Techsystems (ATK) is currently introducing a new AR platform designed for the 6.8 SPC. Which allows for a proprietary 6.8 Magpul P-Mags & an overall cartridge length of 2.32 in. The Personal Defense Weapon (PDW) known as the 'Six8' UCIW (Ultra Compact Individual Weapon) is SPC II w 1:10 in twist and is able to use all current and future 6.8 SPC factory ammunition.

Muzzle velocity from a 24 in barrel

 * 115 gr Full Metal Jacket (FMJ): 2800 ft/s
 * 115 gr Boat Tail Hollow Point (BTHP): 2800 ft/s
 * 115 gr Sierra Match King (SMK): 2800 ft/s

Muzzle velocity from a 16 in barrel

 * 85 gr Barnes TSX ; 3070 ft/s - Silver State Armory (SSA) "tactical" factory load
 * 90 gr Speer Gold Dot 2900 ft/s- Federal(ATK) "tac/mil" load.
 * 95 gr Barnes TTSX: 2850 ft/s - Wilson Combat factory load
 * 110 gr Sierra Pro Hunter; 2575 ft/s - Silver State Armory (SSA) "combat" factory load
 * 110 gr Hornady BTHP TAP; 2550 ft/s - Hornady Law Enforcement "tactical" factory load
 * 110 gr BTHP OTM & Barnes TSX; 2700 ft/s - Wilson Combat factory load
 * 140 gr Berger VLD; 2401 ft/s - Silver State Armory (SSA) factory load

Comparison to other military calibers
Typical trajectory information from carbines with drop and velocity calculated at sea level with a 100 yd zero.

Commercial


For hunters, the 6.8 SPC cartridge is a significant improvement over the 5.56mm (.223) cartridges currently available in the AR-15 platform. The latter cartridges fall below 0.243 in, which is what many counties and states in the USA have chosen as the smallest caliber legal to humanely take medium sized game such as (but not limited to) coyotes, wild hogs, deer, black bear, caribou, and small- to medium-size elk. It is gaining popularity among hog/boar hunters. By adopting 6.8 SPC, a hunter also gains the ability to use the AR-15 platform for hunting out to 300 - 400 yd (depending on load and chamber, out of a 16 in barrel, further with longer barrel). Although, rifles with 12.5 in barrels have been successful at taking deer & wild hogs/boar up to 300 yd (this also depends on load & chamber).

Military/law enforcement adoption
By late 2004 the 6.8x43mm SPC was said to be performing well in the field against enemy combatants in Special Operations. However as of the end of 2012 the cartridge was not used by conventional US military personnel. It was not adopted for widespread use due to resistance from officials on changing calibers and the development of the 6.5 Grendel, which had better accuracy past 500 meters. In 2007, both the U.S. SOCOM and the U.S. Marine Corps decided not to field weapons chambered in 6.8 mm due to logistical and cost issues.

While there are many rumors of evaluations of the cartridge by several major Federal and local law enforcement agencies, the US Drug Enforcement Administration has allowed individual agents to purchase the M6A2 D-DEA - which uses the 6.8 mm Remington SPC - as an authorized alternative to their duty weapon. In 2010 the Jordanian state-owned arms manufacturer KADDB announced that they would be producing 6.8mm rifles and carbines for the Jordanian Army. There is also a contract between LWRC, Magpul, Alliant TechsystemsATK & The Saudi Royal guard for around 36,000 Six8 PDWs & undisclosed amount of ATK/Federal XD68GD (90gr Gold Dot 'training' ammo)and proprietary Magpul 6.8 Pmags specifically for the LWRC Six8.See above under the subsection 'Development' Section. As of 2011, 6.8mm has not gained any major significant military adoption, but it has a notable following among civilian shooters.

Current chamberings
There are currently 4 different chambers for the 6.8 SPC which yield different results. They are: Chamber specifications 3. and 4. are proprietary. Only the rifles chambered with the newer specified chamber (6.8mm Spec II, Noveske Mod 1 and 6.8 ARP chambers) can safely use the higher pressure tactical and near max-maximum handloaded ammunition. Those rifles using the Original SAAMI specs should only be used with the standard commercial cartridge pressure (Specified by SAAMI).
 * 1) The original SAAMI Specifications
 * 2) SPC II
 * 3) 6.8x43mm (renamed 6.8 ARP)(DMR has been replaced by 6.8x43/6.8 ARP,both are/were created by AR Performance.)
 * 4) Noveske Mod 1 designed by Noveske Rifleworks LLC.

Semiautomatic action
The first major manufacturer to offer a 6.8 mm Remington SPC chambered version of the AR-15 was Barrett Firearms Company, offering the Barrett M468 and later the REC7. By 2007, most major manufacturers of AR-15 type rifles for the civilian gun market were offering rifles in this caliber. Dedicated AR upper receiver assemblies chambered for the round are produced by a number of smaller firms. Ruger Firearms produces a 6.8 mm for their Ruger SR-556 piston-driven AR-15 variant. The Stag Arms Hunter and Tactical models utilize the newer chambers and specified twist rates to accommodate higher pressure loadings. Microtech Small Arms Research offers their version of the Steyr AUG in 6.8. Robinson Armament Co. offers the XCR-L in 6.8, which can be easily converted between 6.8, 5.56, and 7.62x39. Bushmaster offers a 6.8 chamber and barrel along with 5.56 for the ACR also. Ruger Firearms chambered their Mini-14 Ranch Rifle in this round for several years; however, it has been discontinued.

Manual action
Remington also makes a bolt-action rifle chambered for 6.8 SPC, a 24 in barrel Model 700. Ruger offers their M77 Hawkeye Compact rifle with a 16.5 in barrel weighing in at 6.0 lb. Browning offers their A-Bolt rifle in 6.8 SPC, and Thompson/Center offers barrels chambered for 6.8 SPC for the G2 Contender and Encore.