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.

Design details

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 (single shot, 3 shot burst, full automatic modes) 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 style 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.

Variants
SIG 716 is battle rifle/DMR variant is made on the same design, but is chambered for the more powerful 7.62x51mm round.

SIG 716 G2 (Generation 2) variant  features a short-stroke pushrod gas system. This operating system reduces carbon fouling, excessive heat and unburned powder in the action, ensuring further improved reliability and function.

Users

 : Used by law enforcement in Argentina.
 : Used by the Special Duty Unit and Counter Terrorism Response Unit.
 : Transitioning into the general service rifle of the Naval Infantry Force.
 : Used By Sa'ka Forces And Navy Thunderbolt 
 : In use with the Georgian MIA and MOD special forces 
 : Order placed for 72,400 units of SIG-716 Patrol G2 model. In December 2019 1st batch of 10,000 rifles were delivered to Indian Army’s Northern Command .
 : Used by PTJ (Counter-Terrorist Unit) of Serbian Police
 : Used by the Police Coast Guard
 : Used by Argovian cantonal police (CTSFO)
 : Used by Royal Thai Army Special Warfare Command and Naval Special Warfare Command
 : Used by Polis Özel Harekat and Presidential Guards
 : Used by Metropolitan Police Counter Terrorist Specialist Firearms Officers (CTSFO) Surrey Police and West Midlands Police
 : 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.