6.8 mm Remington SPC: Wikis

  

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6.8x43mm Remington SPC
Oct. 06 003.jpg
6.8 mm Remington SPC (Left) as compared to the 5.56x45mm NATO cartridge (Right)
Type Rifle
Place of origin  United States
Production history
Designer Remington, SOCOM
Designed 2002-2004
Specifications
Parent case .30 Remington
Case type Rimless, bottlenecked
Bullet diameter 0.277 in (7.0 mm)
Neck diameter 0.298 in (7.6 mm)
Shoulder diameter 0.402 in (10.2 mm)
Base diameter 0.421 in (10.7 mm)
Rim diameter 0.422 in (10.7 mm)
Rim thickness 0.049 in (1.2 mm)
Case length 1.676 in (42.6 mm)
Overall length 2.315 in (58.8 mm)
Ballistic performance
Bullet weight/type Velocity Energy
115 gr (7.5 g) (7.45g) 2,625 ft/s (800 m/s) 1,759 ft·lbf (2,385 J)
Test barrel length: 24 in (609.6 mm)
Source: Remington [1]

The 6.8 mm Remington SPC (or 6.8x43mm) is a rifle cartridge that was developed with collaboration from individual members of US SOCOM.[2] Based upon the .30 Remington cartridge [3], it is midway between the 5.56x45mm NATO and 7.62x51mm NATO in bore diameter and velocity. It is particularly adaptable to current 5.56 mm NATO firearms, the cartridge overall length being comparable.

Though ballistically similar to the 1950s-era .280 British, improved propellant powders allow the 6.8 mm to have a smaller case. The 6.8 mm SPC (Special Purpose Cartridge) has a muzzle velocity of 2,625 feet per second (800 m/s) from a 16 inch (406 mm) barrel using a 115-grain Hornady OTM bullet.[4]

Contents

Development

The 6.8mm SPC cartridge was designed to address the deficiencies of the terminal performance of the 5.56x45mm cartridge currently in service with the U.S. Armed Forces.[5] 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.[6] The development of this cartridge is remarkable in that it was designed by actual shooters in the armed forces, instead of by industry professionals. The goal was to create a cartridge that would bridge the gap between 5.56mm and 7.62x51mm, something that would perform similarly to the Soviet bloc 7.62x39mm AK-47 cartridge.

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.[7]

In tests, it was determined that a 6.5mm projectile had the best accuracy, but a 7mm projectile had the best terminal performance. Further tests showed that a 6.8mm projectile 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 cartridge, with the new cartridge proving to be about 200 feet per second faster.[8] The resulting cartridge was named the 6.8 Remington Special Purpose Cartridge due to the size of its projectile and the fact that it was based on the .30 Remington case.

In theory, the new cartridge only requires switching the barrel, bolt and magazine of a rifle chambered in 5.56mm, but almost all parts manufacturers sell complete upper receiver assemblies chambered for 6.8SPC along with individual parts. While it's somewhat more expensive, it makes converting an existing 5.56mm/.223 rifle to 6.8SPC take less than a minute without any tools being required. In contrast, considerable gunsmithing skill, tools, and time are required to detach the barrel from the upper receiver and the gas system. Reconnecting the new barrel is not trivial, either.

Performance

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% greater energy than the 5.56 mm NATO (M4 configuration) at 100-300 meters. The 6.8mm SPC is ballistically inferior to the 7.62x51mm NATO cartridge; however, it has far less recoil, is considerably more controllable in rapid fire, and much lighter, allowing operators to carry more ammunition than would otherwise be possible with the larger caliber round. The 6.8 mm generates around 1,759 ft·lbf (2385 J) of muzzle energy with a 115 grain bullet. In comparison, the 5.56x45mm round (which the 6.8 is designed to replace) generates around 1325 ft-lbf (1,796 J) with a 62 grain bullet, giving the 6.8mm a terminal ballistic advantage over the 5.56mm of 434 ft-Ibf (or 589 J). In recent developments (the period 2004-2008) the performance of the 6.8SPC has been increased by approximately 200 ft/s by the work of one ammo manufacturer and a few custom rifle builders using the correct chamber and barrel specifications. The velocities obtained now from an 8" barrel are equal to what a 16" barrel was producing 4 years ago and the 16" barrel velocities are equal to what a 24" barrel produced 4 years ago using the data below. By increasing the velocity of the ammo 200 ft/s the range of terminal effectiveness has been increased approximately 100 yards or an 8" barrel now has the same effective range as a 16" barrel had in 2004 as the 6.8 loses apx 25ft/s/inch. -SSA website and 6.8 Performance test verified[9].

It should be noted that there are 2 standardized, but different, chambers for the 6.8 SPC which yield different results. Only the rifles chambered with the newer specified chamber and the slower barreling twist rate can safely use the higher powered/higher pressure ammunition. All other rifles should only be used with the standard cartridge pressure loadings.

Muzzle velocity from a 24-inch (610 mm) barrel

  • 7.45 g (115 gr) Full Metal Jacket (FMJ): 2,625 ft/s (800.1 m/s)
  • 7.45 g (115 gr) Boat Tail Hollow Point (BTHP): 2,624 ft/s (799.8 m/s)
  • 7.45 g (115 gr) Sierra Match King (SMK): 2,625 ft/s (800.1 m/s)

Muzzle velocity from a 16" barrel in 2009

  • 85gr Barnes TSX ; 3030 ft/s- "tactical" factory load
  • 110gr Sierra Pro hunter; 2575 ft/s- "combat" factory load

Comparison to other military calibers

Cartridge Muzzle velocity 200 yards drop 200 yards velocity 400 yards drop 400 yards velocity
.223 55gr M193 3073 fps 2.2 inches 2353 fps 27.8 inches 1743 fps
.223 77gr OTM 2679 fps 3.3 inches 2216 fps 32.7 inches 1810 fps
6.8 SPC 115gr SMK 2650 fps 3.5 inches 2143 fps 35.4 inches 1677 fps
6.8 SPC 110gr V-MAX 2650 fps 3.3 inches 2208 fps 31.1 inches 1811 fps
7.62x39mm 2300 fps 3.3 inches 1787 fps 53.8 inches 1324 fps
.308 168gr SMK 2600 fps 3.4 inches 2235 fps 32.3 inches 1891 fps

Typical trajectory information from carbines with drop and velocity calculated at sea level with a 100 yard zero.[1]

Applications

Commercial

For hunters, the 6.8 SPC cartridge is a significant improvement over the 5.56mm and .223 cartridges currently available in the AR-15 platform. The latter cartridges fall below .243 of an inch, which is what many states have chosen as the smallest caliber legal to humanely take medium sized game such as deer. By adopting 6.8 SPC, a hunter gains the ability to use the versatile and ergonomic AR-15 platform for hunting.

Military/law enforcement adoption

So far there is no confirmed adoption of the caliber by the U.S. military.

While there are many rumors of evaluations of the cartridge by several major Federal and local law enforcement agencies, it has not been confirmed to be in service with any official agency yet.

Current chamberings

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 REC7. By 2007, most major manufacturers of AR-15 type rifles for the civilian gun market, such as Bushmaster Firearms International, LWRC, DPMS Panther Arms and Rock River Arms were also producing 6.8 mm Rem SPC carbines. Ruger Firearms produces a 6.8 mm version of their popular Ruger Mini-14 series carbine. [10] Remington also makes a bolt-action rifle chambered for 6.8 SPC, a 24" barrel Model 700. Stag Arms offers several AR-15 based rifles chambered in 6.8 SPC. The Stag Arms Hunter and Tactical models utilize the newer chambers and specified twist rates to accomodate higher pressure loadings. Microtech Small Arms Research offers their version of the Steyr AUG in 6.8. 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. Robinson Armament offers the XCR-L in 6.8, which can be easily converted between 6.8, 5.56, and 7.62x39.

See also

Notes

  1. ^ Remington Web Page: 6.8 SPC Velocity/Ballistics
  2. ^ Not a private endeavor or fully sanctioned government project
  3. ^ 30 Rem
  4. ^ http://www.dtic.mil/ndia/2004arms/session3/dennison.ppt
  5. ^ http://www.globalsecurity.org/military/systems/munitions/68spc.htm
  6. ^ http://demigodllc.com/articles/6.8-mm-spc-cartridge-history-development-hornady-stag-arms-carbine/
  7. ^ http://www.rifleshootermag.com/ammunition/remington_0303/
  8. ^ http://demigodllc.com/articles/6.8-mm-spc-cartridge-history-development-hornady-stag-arms-carbine/?p=2
  9. ^ 6.8 Performance test
  10. ^ Information on the 6.8 SPC Mini

External links








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