The 6.8 SPC was designed to address the deficiencies of the
terminal ballistics of the
5.56×45mm NATO cartridge currently in service with the armed forces of all
NATO-aligned countries. The cartridge was the result of the Enhanced Rifle Cartridge Program. The 6.8 SPC (6.8×43mm) was initially developed by Master Sergeant Steve Holland and Chris Murray, a United States Army Marksmanship Unit gunsmith, to offer superior downrange lethality over the 5.56 NATO/.223 Remington in an M16-pattern service rifle with minimal loss of magazine capacity and a negligible increase in recoil. 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 comparing various caliber bullets using a .30 Remington parent case, Holland and Murray determined that a 6.5 mm
caliber projectile had the best accuracy and penetration, with historical data going back for decades of
US Army exterior and terminal ballistic testing, but a 7 mm projectile had the best terminal performance. The combination of the cartridge case, powder load, and projectile easily outperformed the
7.62×39mm and
5.45×39mm Soviet cartridges, with the new cartridge's muzzle velocity proving to be about faster than the 7.62x39. The 6.8mm Remington SPC was designed to perform better in short-barreled
CQB rifles after diminished performance from the 5.56 NATO when the M16A4 was changed from the rifle configuration to the current
M4 carbine. The 6.8 SPC delivers 44% more energy than the 5.56mm NATO (M4 configuration) at . The 6.8mm SPC is not the ballistic equal of the 7.62×51mm NATO cartridge, but it has less recoil, has been said to be more controllable in rapid fire, and is lighter, allowing operators to carry more ammunition than would otherwise be possible with the larger caliber round. The 6.8 mm generates around of muzzle energy with a bullet. In comparison, the 5.56×45mm round (which the 6.8 is designed to replace) generates around with a bullet, giving the 6.8 mm a terminal ballistic advantage over the 5.56 mm of . One of the enigmatic features of this cartridge is its being designed for a shorter-barrel carbine-length rifle than the standard rifle length is (usually ). The round only gains about for every 25 mm of barrel length past the standard barrel (all else being equal) up to barrel lengths around with no gain or loss in accuracy. It also does well in rifles with less than barrels. In recent developments (the period 2008–2012) the performance of the 6.8 SPC has been increased by approximately by the work of ammunition manufacturer Silver State Armory LLC (SSA) and a few custom rifle builders using and designing the correct chamber and barrel specifications. The 6.8mm Remington SPC cartridge weighs, depending on the manufacturer and load, between . Also, more recently,
LWRC,
Magpul and
Alliant Techsystems (ATK) introduced a new AR-15 designed for the 6.8 SPC which allows for a proprietary 6.8 Magpul P-mags and an overall cartridge length of . The personal defense weapon (PDW) known as the "
Six8" is an SPC II with 1: twist and is able to use all current 6.8 SPC factory ammunition.
Muzzle velocity from a barrel Muzzle velocity from a barrel Muzzle velocity from a barrel Comparison to other military calibers Typical trajectory information from carbines with drop and velocity calculated at sea level with a zero. ==Applications==