SIG SAUER SIGM400 Rifle - Manual (Page 21)

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2.0. Mechanical Characteristics and Rifle Theory
2.1 Rifle Description
2.1.1 General
The SIG M400 rifle is a direct impingment rifle with a rotary bolt mechanism capable of semi-automatic or full automatic
fire operation. Semi-Automatic is defined as one round being fired each time the trigger is pressed to the rear until the
magazine is depleted of ammunition. The rifle is chambered in 5.56x45mm NATO and is compatible with .223 Remington
ammunition.
2.1.2 Barrel, Receiver and Gas System
The barrel is mechanically mated to the receiver by means of a barrel nut, and the barrel extension. The flash suppressor
if applicable is screwed onto the muzzle end of the barrel via ½ x 28 TPI thread pattern. The front sight housing, which is
fitted to the barrel, contains the gas port and the front sight. The upper receiver has an integral M1913 accessory rail for
attachment of sights or optics.
FIG 1 BARREL WITH RECEIVER AND GAS SYSTEM
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