Weapon Name- Mk. 8 Mod 2
Round Type- 6.8mm Remington
Over-all length- 30-33 inches (762mm-838.2mm)
Barrel length- 14.5 inches
Weight- 6.5 lb
Rate of Fire- 600 RPM
Feed Mechanism- Detachable Box Magazine
Round Capacity- 28, 30, 100
Effective Range- 300 meters
Range- 600 meters
Accuracy- 1.3 MOA
Accessories- Picatinny Rails
Quick switch firing mechanism- N/A
Scope/Sights- Picatinny Rails
Muzzle Velocity- 785 m/s, 7.45 grams, 2,295 joules
Firing System- Short Stroke Gas piston
Miscellaneous/electronic information- The weapon is essentially an XM8 with a few minor changes chambered in 6.8mm remington.
Basic Information
The weapon is essentially an XM8 with a few minor changes chambered in 6.8mm remington. The XM8 uses an extremely reliable short stroke gas piston, which is substantially more reliable than direct impingement systems, while still possessing the same level of accuracy and low recoil. Compared to long stroke gas pistons, the weapon has a lighter bolt and piston mass and a shorter action, which reduces the recoil significantly, while still retaining much of the high reliability and durability. Key differences with the original XM8 are ambidextrous controls, a quick adjustable right or left ejection port, a slightly shorter folding stock compatible with AR-15 furniture, being STANAG compatible, and a higher degree of modularity. While the original XM8 was designed to work with form fitting pieces to increase their cohesion with accessories and the weapon, to provide greater ergonomics and reduced weight, it lacked standard modularity available from equipment such as picatinny rails. This firearm possesses the option for the same close fitting accessories, however it also possesses optional picatinny rail attachments, with keyhole mounting, that allows the picatinny rails to mounted to the firearm. This opens up the weapon to being able to use a variety of different weapon attachments, such as lasers or scopes. It possess a lower profile top rail, instead of the raised rail found in the traditional XM8, as well as a non-reciprocating, fixed non-folding charging handle. The slimmer profile as well as changed accessories makes the weapon lighter, or approximately 1 pound lighter than a standard XM8.
The weapon is essentially patterned off of the XM8, however it utilizes the 6.8mm Remington SPC. The short stroke gas piston is considered to be more reliable than direct impingement systems while retaining the same low recoil and high accuracy, and in general is more smoothly operating than long strike gas pistons (less recoil, muzzle rise, and higher accuracy). The firing system is based off of the XM8 which uses a short stroke gas piston system, similar to that in the AR-18, FN SCAR, or XM8 In July 2007, the US Army announced a limited competition between the M4 carbine, FN SCAR, HK416, XCR, and the previously-shelved HK XM8. Ten examples of each of the four competitors were involved. Each weapon fired 60,000 rounds in an "extreme dust environment." The purpose of the shoot-off was for assessing future needs, not to select a replacement for the M4. The XM8 scored the best, with only 127 stoppages in 60,000 total rounds, the FN SCAR Light had 226 stoppages, while the HK416 had 233 stoppages. The M4 carbine scored "significantly worse" than the rest of the field with 882 stoppages. Over-all this gives the weapon between 4-8 times higher reliability than the M4 carbine or similar firearms, with a variety of operating conditions being less hazardous to the over-all functioning of the firearm, including sandy or wet condition. The weapon also has substantially higher heat tolerance than most firearms, even higher than most similiar firearms. While an M16 is only expected to be able to realistically fire 15-20 rounds a minute, the XM8 can fire over 80 rounds per minute with relatively little difficulty, which is roughly equal to the firing rate of the M249 machine gun, and twice that of the M27 IAR at 36. Heckler and Koch engineers fired 4 high-capacity magazines, with 100 rounds apiece, in less than 5 minutes from their XM8 entrant, or 400 rounds in less than 5 minutes.
The weapon uses a detachable polygonal cobalt chrome "flow formed" 6 groove 1:11 (1 complete turn in 1 in 11 inches / 279.4mm) right hand turn barrel; the barrel is made of an alloy that contains more than 50 percent cobalt. The barrel is roughly 13% heavier than standard steel barrels, but is more erosion and corrosion-resistant and is designed to retain high strength during long-term exposure to high temperatures. Cobalt alloys are frequently used in the aerospace industry, such as the hot-gas section of turbine engines. A proof of concept M240 7.62mm x 51mm NATO barrel, in practice, had 24,000 rounds test-fired through it, causing it to reach temperatures of 1,100 degrees, without failure. A steel barrel would have failed under such treatment. The barrel itself, combined with polygonal rifling, is extremely durable, and has a minimum 20,000 round barrel life, although it is possible to extend this or get use out of the rifle after the minimum is reached. The barrels come in 10, 14.5, and 20 inches.
The 6.8mm Remington SPC in use with the weapon, can achieve 1.3 MOA. The weapon uses a 7.45 gram round that travels at approximately 785 m/s, or generates 2,295 joules, in the longest barrel configuration. This is approximately 15% more power than an Ak-47, and 30% more than an M16, at the muzzle. Tests by the U.S. military showed that 6.5mm cartridge size had the best accuracy of their intermediate cartridges tested, while the 7mm cartridges had the best terminal ballistics; the 6.8mm Remington was considered the best compromise between the two. While less accurate and with a shorter range the 6.5mm Grendel, it's velocity and accuracy from incredibly short barrels is significantly greater, which makes it ideal to short, carbine like weapons, and better for close quarters combat. This is still much better than the 5.56m or 7.62mm x 39mm, while fitting in similarly sized weapons, which makes it thus it's size and power, in addition to accuracy, a generally superior cartridge than either, combining both the strengths from each cartridge. In addition to it's high ballistic coefficient, provides, barrier penetration, and accuracy over traditional 5.56mm weapons, making the weapon very effective at ranges of approximately 500 meters.
Each barrel possess a muzzle break designed after the surefire muzzlebreak. Though there are numerous ways to measure the energy of a recoil impulse, in general a 10% to 50% reduction can be measured. Besides reducing felt recoil, one of the primary advantages of a muzzle brake is the reduction of muzzle rise. This lets a shooter realign a weapon's sights more quickly. This is relevant for fully automatic weapons. The weapon also possess a hydraulic recoil buffer similiar to that in the M249. The, the design of the weapon and it's straight back recoil impulse, as well as the tighter, more steady grip on the weapon, combined with the impact gel recoil pad, makes the weapon very easy to use and relatively comfortable. The weapon uses a Blackbox round counter that can be hooked up to an LCD screen to show the rounds remaining. The magazines are generally color coded, which provides indication of how many rounds are within each magazine, although loading in another magazine that does not meet the criteria can result inaccurate round counting predictions; the round counter mechanism itself, however, will not falter. The weapon is made from composites and polymers similar to the P90 and XM8, to both reduce the cost and weight as of the weapon, as well increase the durability. The weapon fires from a closed bolt for both maximum accuracy and reliability. The weapon has picatinny rails, and thus an array of different sights are available for the weapon.
The weapon also utilizes very similiar magpul magazines, however specifically based off of the XM8. The magazines are known for their higher reliability and tendency to reduce jams; the magazine well on STANAG compatible magazines tends to be unnecessarily large and long, occasionally causing feeding issues. In an extreme dust test with the M4 carbine, out of the 883 jams approximately 239 were a result of the magazine; approximately a quarter of the jams of the jams were caused by magazine malfunctions, most commonly double feeding. This comparable to the entire FN SCAR or Hk416 jam rate. Superior magazines have the ability to eliminate up to half the jams frequently found in piston operated weapons, or more; thus, the improved magpul magazines can help prevent a significant number of jams when utilized with the weapon, particularly considering the higher level of reliability of the firing system. The weapon uses a much larger lever activated magazine release, which is similiar to the Ak-47 in terms of durability and strength, but as easy to activate as standard STANAG magazines. By using the lever, the mechanism can hold significantly heavier magazines, such as 100 round drum magazines, or can allow the soldier to support their full weight on the weapon (without it breaking), while still being as ergonomic and simple to use as the M16 series of weapons.
