SIG Sauer SIG516

The SIG Sauer SIG516 is a firearm manufactured by SIG Sauer. The rifle is based on the earlier 5.56×45mm NATO AR-15 and the M16.

Operating mechanism
The SIG516 is a semi-automatic multi-caliber rifle, intended for civilian and law enforcement markets. The same family also includes selective-fired assault rifles, strictly intended for law enforcement and military use. It fires from a closed bolt, and has a short-stroke push rod piston system. The gas piston pushes the bolt carrier rearward, where it is returned to the forward and locked position by a spring. This process loads the next cartridge. The 516 has a four position gas regulator, allowing the user to choose the amount of gas directed to the piston.

Features
The SIG516 has a safety lever on the left side, to be used by the thumb of the shooting hand. The gas block integrates an adjustable gas regulator. The front gas block is railed to accept the front sight with a flip-up sight post. SIG516 models are equipped with an M16A2 style bird-cage flash hider.

All SIG516 models except the Marksman are equipped with 16 inch barrels shrouded by a free-floating M1913 Picatinny rail, as well as flip-up iron sights (BUIS) made by SIG Sauer.

The 5.56×45mm NATO SIG516 models accept AR-15 style box magazines. These magazines are constructed in 5-, 10-, 20-, and 30-round variants. SIG516 Russian rifles must use a different magazine, as they are chambered in 7.62×39mm. The SIG516 Russian uses magazines designed for 7.62×39mm AR-15 rifles. The rifle is hammer-fired and has a two-stage trigger mechanism in the SIG516 Marksman, while all others have a military specification single-stage trigger.

A bolt hold-open device locks the bolt carrier assembly open after expending the last cartridge from the magazine and is released by pushing the bolt catch lever located on the left side of the receiver. Alternatively, a left-handed shooter may release the bolt by pulling the charging handle a short distance to the rear.

Users

 * 🇭🇰 Hong Kong - In use with the Hong Kong Police Special Duties Unit and Counter Terrorist Response Unit (CTRU)
 * Georgia - In use with the Georgian MIA special forces
 * 🇲🇽 Mexico - Currently replacing the M16 rifles in use by the Naval Infantry Force of the Mexican Navy.
 * 🇷🇸 Serbia - Used by PTJ
 * 🇸🇬 Singapore - Used by Protective Security Command and Police Coast Guard Special Task Squadron.
 * 🇨🇭 Switzerland - used by Cantonal police Argovia (CTSFO)
 * 🇹🇷 Turkey - Used by Polis Özel Harekat and Presidential Guards
 * 🇬🇧 United Kingdom - used by Metropolitan Police Counter Terrorist Specialist Firearms Officers (CTSFO) and West Midlands Police
 * 🇺🇸 United States - Used by Delaware State Police when purchased in 2012 and also by Cincinnati Police Department SWAT, as well as the Anderson County, South Carolina Sheriff's Office SWAT. San Diego Police Department SWAT, in which the rifles will replace out aging Vietnam era M16s.