(manufacturer calls it an "operating rod"), extending into the handguard. The gas key contains the return spring which is fixed between the front of the receiver and the collar at the front of the gas key. The gas port is under the back side of the gas block, gasses go up then forward to the front side of the gas block then up and back to the gas tube. The gas tube is about half of the length of a standard AR-15 tube. The gas tube is always inside of the gas key (minimal overlap is about 1 inch). This leaves the area near the bolt much cleaner. Almost all gasses exit the gun through the holes on the right side of the bolt carrier, and minimal leaks from the gas key to the handguard area do not hinder the gun's function. Upper To accommodate the unique forward buffer and gas impingement system, the proprietary upper is taller and thicker than a standard AR upper. The handguard rail has a removable top cover to access the recoil spring system for disassembly. The charging handle is proprietary and has a beefier design to fit the op-rod. Models LR-300 ML-A: Military/law enforcement model (selective fire version). Has an barrel, aluminium forend, and fires single shots or bursts. LR-300 ML-N: Military/law enforcement model (selective fire version). Has an barrel, Nylatron forend with attachable Picatinny rails, and fires single shots or bursts. LR-300 SR-A: Sport rifle model (semi-auto fire version). Has a barrel, aluminum forend, and fires single shots. LR-300 SR-N: Sport rifle model (semi-auto fire version). Has a barrel, Nylatron forend with attachable Picatinny rails, and fires single shots. LR-300 AXL: Aluminium quad handguard. LR-300 AXLT: Aluminium partial handguard. LR-300 NXL: Nylatron handguard. TTR-XA: Handguard with full length aluminium quad rail. TTR-XAS: Aluminium handguard partially fitted with picatinny rails on bottom and sides at 90 mm (3.5 inches) of its length. TTR-XASF: Aluminium handguard partially fitted with picatinny rails on bottom and sides, fixed stock. TTR-XN: Nylatron handguard. See also SIG MCX, another folding stock AR-15 style rifle References External links Image of an LR 300 equipped with a bipod. POLICE magazine - Weapons - Reviews:Arsenal - Para USA Tactical Target Rifle (2009) 5.56 mm assault rifles ArmaLite AR-10 derivatives