Weapon Name- P90- 5.56mm
Round Type- 5.56mm Caseless
Over-all length- 20 Inches (508mm)
Barrel length- 12.5 inches (317.5mm)
Weight- 2.54 kg (5.60 lb) empty, 2.68 kg (5.9 lb) empty magazine, 3.1 Kg loaded (6.8 lb)
Rate of Fire- 900 rounds/min
Feed Mechanism- Top-Fed Magazine
Round Capacity- 50
Effective Range- 400 meters (Between 300 and 650 meters for greatest wound potential)
Range- 850 meters
Accuracy- .75 MOA at 300 meters (1.5 MOA at 750 meters)
Accessories- Picanty Rail
Quick switch firing mechanism- N/A
Scope/Sights- Picanty Rail
Muzzle Velocity- 920 m/s
Firing System- LR-300 self folding direct impingement
Miscellaneous/electronic information- Basically a P90 refitted to fire 5.56mm rounds and a different firing mechanism designed to compensate for the increase in recoil and pressure.
Basic Information
The weapon is essentially a a P90 body refitted to fire 5.56mm rounds with a different firing mechanism designed to compensate for the increase in recoil and pressure. While ordinarily a P90 platform would probably be incapable of firing 5.56mm NATO rounds, despite the similarity in caliber size, an upgraded firing system, the LR-300's direct impingement system, allows for a smaller, nearly recoiless firing system to serve as the heart for a small P90 Carbine and allow it to fire 5.56mm NATO rounds. While ordinary problems with the direct impingement system can never be completely eliminated, becuase the P90 fires from a completely closed bolt and uses extremely clean firing propellants, it is just as likely to jam as an original M16 (I.E. one of the ones before their introduction into Vietnam, where they used different propellants and fired in "Dirty" Environments).
The barrel is a 12-inch (318 mm) polygonal match-grade free floating stainless steel heavy barrel with a 1:7 (178 mm) rifling twist ratio as standard for the SPR. The barrels are manufactured by Douglas Barrels with a special contour to maximize accuracy and to minimize weight. An OPS Inc. muzzle brake and collar (to align the OPS Inc. 12th Model Suppressor) is installed with the barrel. These barrels were designed to take advantage of the new Mk 262 cartridge, which uses a 77-grain (5 g) bullet. While a 12.5 inch barrel is usually incompetent to fire a 5.56mm round, like in the XM8, it uses polygonal rifling that allows to capture more of the expanding gases (as a polygonal barrel is closer to a circle than a rifled barrel with grooves etched into it) and reduces the over-all friction on the bullet, making it a much more effective bullet from a shorter barrel.
The rounds of course, have slightly lower pressure when compared standard 5.56mm x 45mm NATO rounds. This is becuase the rounds fired are caseless, requiring the gun itself (or the breach) to take all the pressure without breaking. While only a marginal decrease, it's enough to allow cheaper materials to be exploited rather than more expensive materials. The round is fired from the typical LR-300 firing system, however, instead of using a case like in a regular round, the gun uses the steel breech to build the pressure required to fire the round. The hammer, of course, seals off the barrel completely when it enters the breech. The gun has a firing life of roughly 10,000 rounds.
