Tactical assault rifles SIG Sauer MCX and SIG Sauer 516 – full ‘autopsy’

This post was published in GunsReview. The point of view expressed in this article is authorial and do not necessarily reflect BM`s editorial stance.


PANAGYURISHTE, (BM) – In this issue, we will get acquainted with the tactical rifles SIG Sauer MCX and SIG Sauer 516, or rather their modifications – SIG Sauer MCX Carbine and SIG Sauer 516 Patrol. The rifles are manufactured in the USA, at the facilities of SIG Sauer and are produced in both the military version and the version for the commercial civilian market.

The difference between the military and “civilian” options is the presence of an automatic firing mode. The rifles are provided by SIG Sauer’s Official Exclusive Representative, Tactical Systems, and this review was filmed at the new Mil Dot store featuring the SIG Sauer MCX Carbine and SIG Sauer 516 Patrol rifles.

The SIG Sauer 516 rifle was first presented at the largest weapons exhibition Shot Show in 2010. Today, the second generation of this SIG Sauer 516G2 rifle is being produced, with a slightly modified design, an improved barrel, a modified principle of its attachment and an improved gas valve.

SIG Sauer MCX is an absolute novelty for 2016 from SIG Sauer – its presentation was only a year ago – this happened in January 2015, again at the Shot Show. The SIG Sauer 516 and SIG Sauer MCX were designed as weapons for the US Army and Police Special Forces.

The design of the SIG Sauer 516 and SIG Sauer MCX rifles combines the widely used and popular design of the AR-15 and the German-Swiss approach to high quality and reliability, which is embodied in the principle of operation of the rifles, namely in the principle of operation that differs from the rifles of the AR-15 family gas venting mechanism.

But first things first…

The complete set of rifles SIG Sauer 516 and SIG Sauer MCX is typical. The package includes:

  • cardboard packaging
  • user’s manual
  • 3 shot cartridges and a certificate from the forensic center
  • belt
  • cleaning kit

The SIG Sauer 516 and SIG Sauer MCX rifles are available for the following ammunition:

SIG Sauer 516 is produced only for the use of 5.56×45 NATO ammunition; The SIG Sauer MCX rifle can use 5.56×45 NATO (.223 Rem) and .300 BLK7 ammunition, and it is also planned to produce rifles for the use of the 7.62×39 caliber popular in our latitudes.

The SIG Sauer MCX rifle, in contrast to the SIG Sauer 516, which is produced in a single standard version, is produced in 3 modifications, these are:

  • SIG MCX SBR – rifle with 9 ”barrel and folding frame stock;
  • SIG MCX Carbine – an army carbine with a 16 ”barrel and a folding frame stock;
  • SIG MCX Pistol W / PSB – a rifle with a 9 ”barrel and a folding multifunctional stock with the ability to attach to the shooter’s forearm.
    All three SIG MCX modifications can use .300 BLK, 5.56 × 45 NATO and 7.62×39 ammunition.

The SIG Sauer 516 and SIG Sauer MCX rifles are built from high-strength aircraft-grade aluminum and anodized top and bottom receivers. The upper receiver of the SIG Sauer 516 is made with an integrated platform with a Picatinny rail for attaching 15 cm long shooting accessories.

On the upper receiver of the SIG Sauer MCX, the Picatinny rail is 30 cm long. The lower receiver of the SIG Sauer MCX is made with an integrated trigger guard and, thanks to its dimensions, allows the use of shooting gloves without any problems.

On the SIG Sauer 516, a plate acts as the trigger guard, which, if necessary, and this, for example, the use of oversized gloves in the winter, can provide more space in the trigger area. To do this, press the spring-loaded catch on the front right side and turn the plate down.

For safety reasons, this operation must be carried out immediately before firing and after that return the plate to its original, “closed” state. The lower receivers of both rifles structurally allow the use of any pistol grips of the AR-15 standard.

The handles are made of polymer. The angle of the handles is quite comfortable, the handles are anti-slip stamped. The grips are hollow inside and can be used as pencil cases.

SIG Sauer 516 and SIG Sauer MCX magazine receptacle shafts are angled to facilitate quick magazine attachment. The MCX magazine receptacle shaft is widened at the bottom in the form of a skirt, which serves as a kind of magazine movement guides.

The mine on the SIG Sauer 516 is straight. For better ergonomics, the magazine receptacles of both rifles are made with smooth edges.

The magazine is connected by its direct upward movement. Thanks to the magazine shaft skirt on the SIG Sauer MCX, its attachment takes place without any problems and delays, even if the initial angle of the magazine movement is not straight.

The attachment of the magazine on the SIG Sauer 516 is also quite fast and does not require detailed orientation of the direction of movement of the magazine.

On the right side of the upper receiver there is a case ejection window equipped with a protective metal shutter to prevent the ingress of dust and dirt. The shutter is spring-loaded and mechanically synchronized with the movement of the shutter – it opens when the shutter is cocked.

In the rear part of the upper receiver of the SIG Sauer 516 and SIG Sauer MCX there is an auxiliary rammer, which allows mechanical force to send the cartridge into the chamber in case of its “under-delivery” when feeding from the magazine or incorrect operation of the shooter when cocking the bolt cocking handle.

Two position fuse switch. This safety element on the SIG Sauer MCX and SIG Sauer 516 is double-sided, directly above the fire control stick. The location of the switch and its operating positions allow you to very quickly bring the carbine into readiness for firing.

The thumb of the holding hand, and this is also true for the shooter with the left dominant hand, is in close proximity to the safety catch and when the grip is formed, the safety flag is quickly transferred from the horizontal (“Safe”) to the vertical (“Fire”) position by the natural movement of the thumb. When set to the safety catch, the trigger is blocked.

On the left side of the center of the lower receiver on the SIG Sauer 516 and SIG Sauer MCX there is a shutter delay button. Its placement is also standard for the AR-15 line. The functionality of the button on the SIG Sauer MCX, in addition to canceling the slide delay, allows setting the slide delay.

To do this, you must press the enlarged area of ​​the lower part of the key, after having moved the bolt back with the cocking lever. Setting on the slide delay also occurs when the ammunition runs out.

The location of the cocking lever is standard for this rifle and carbine format. The only caveat that fans of the AR-15’s layout will notice is that the lever is moved closer to the top of the receiver. This is due to the principle of operation of rifles, which differs from the classic AR15, namely, the use of a gas piston scheme. The shutter cocking lever is made of metal.

The cocking lever handle on the SIG Sauer MCX is equipped with two interlock keys, which will make it comfortable to use with both right and left hands. The cocking lever on the SIG Sauer 516 is a classic one with one interlock button.

Another difference between the SIG Sauer 516 and the SIG Sauer MCX is the stock options. The SIG Sauer 516 is equipped with a telescopic stock and the SIG Sauer MCX with a folding stock. The SIG Sauer 516 stock consists of a recoil buffer tube, which also serves as a guide, and a shoulder rest.

Adjustment of the buttstock length is carried out using the locking lever located in the stop window. The possible adjustment range is 5 positions, which allows to increase the stock length by 18 – 34 – 50 – 68 and 84 mm. The SIG Sauer MCX stock is a folding frame stock and is equipped with a swivel joint that also acts as a retainer.

The butt is folded to the left, for this it is necessary to raise the butt frame up, release it from fixation and fold the butt.

The shoulder rests of the butts are equipped with shock-absorbing rubber pads. The SIG Sauer 516 and SIG Sauer MCX rifles are equipped with a pistol grip and stocks from SIG Sauer’s own production.

The SIG Sauer 516 rifles are available with a 7.5 ”barrel; ten”; 14.5 ”, 16” and the SIG Sauer MCX are equipped with 9 ”and 16” barrels.

The barrels are free-hanging, with chrome channels and are manufactured to military standards (Mil Spec). Barrels are treated with a special Nitride coating for added protection.

The number of rifling of the barrel is 6, and the pitch of the rifling of the barrel depends on the ammunition used:

  • on barrels designed for use with 5.56×45 NATO rifling pitch 1: 7 “;
  • on barrels intended for the use of ammunition of caliber 7.62×39 – 1: 9.5 “;
  • on barrels designed for use with .300 BLK rifling pitch 1: 6 “.

The design of the SIG Sauer 516 and SIG Sauer MCX allows for the ability to change the barrel, and this can be done in the field and without a set of special tools. In the factory configuration, the barrels are equipped with flame arresters, and provide for the possibility of attaching a silencer

A gas block is installed on the barrel, but its design differs from that of other rifles and carbines using the AR15 layout. The gas block SIG Sauer 516 and SIG Sauer MCX are equipped with an adjustable gas valve. Adjustment, using the SIG Sauer 516 as an example, is performed by moving the gas valve handle to one of the 4 positions.

The following valve installation modes are provided:

  • Normal – shooting under normal conditions;
  • Unfavorable – with a contaminated rifle, poor quality ammunition or an unfavorable environment;
  • Suppression – shooting with a silencer. It is a partial shutdown of the gas system.
  • Disabled – completely disables the gas system and uses the rifle exclusively with single firing mode.

The next element of the SIG Sauer 516 and SIG Sauer MCX rifles is a quad-platform for mounting shooting accessories, which also serves as a forend. On the SIG Sauer 516 the platform consists of a top and bottom element, on the SIG Sauer MCX it is a lightweight aluminum frame structure that attaches directly to the bottom and top receivers and is secured with a pin in front of the lower receiver.

Next, consider the “internal” design features of the rifles. Disassembly of both rifles is carried out according to the typical AR15 scheme, but taking into account a different gas vent mechanism with some peculiarities. For disassembly it is necessary (in detail in the video):

  • check the rifle for the presence of a cartridge in the chamber;
  • remove the pins at the rear of the lower receiver and separate the two main elements of the carabiner.

One of the interesting features of the connection between the receivers on the SIG Sauer 516 and SIG Sauer MCX rifles is the spring-loaded stem in the inner cavity of the lower receiver.

With its help, when connecting the upper and lower receivers, backlash is eliminated and a sense of the integrity of the connection of these rifle elements is achieved.

  • further, to dismantle the quad-platform on the SIG Sauer MCX, you need to remove the pin in the front of the lower receiver and simply move the platform forward;
  • move the bolt cocking handle back a little distance, remove the frame with the bolt (on the SIG Sauer MCX, the frame with the bolt and return springs) and remove the bolt cocking handle ..

To disassemble the shutter, you must:

  • SIG Sauer MCX – disconnect the return springs from the guides;
  • remove the striker mounting pin on the left side of the frame with the bolt and remove the striker;
  • turn the cam pin of the bolt fastening and remove the bolt.
  • to detach the platform on the SIG Sauer 516 rifle, first of all, you must remove the gas piston. To do this, press the button located at the end of the gas block, turn the head of the gas piston counterclockwise and remove it;
  • then on SIG Sauer 516 it is necessary to unscrew 2 screws securing the platform to the lower receiver, 4 screws connecting the upper and lower platform elements and remove them;

In a disassembled view, we can see directly the gas vent mechanism itself, which structurally distinguishes these rifles from the “classic” AR15 with a gas vent mechanism developed by Eugene Stoner.

Instead of a long gas tube above the barrel with a direct gas outlet to the breech block used in the AR15 design, the automatic venting system uses a separate gas piston. The MCX rifle has a short stroke piston and the entire assembly is much smaller than the SIG Sauer 516 design.

Considering the structural differences of the assembled gas piston, the bolt frame design also differs in rifles. The piston, after firing, through a special rod, transmits an impulse of the pressure of the powder gases to the frame with the shutter, thereby realizing its movement.

This implementation of the gas venting mechanism allows for more stable and reliable operation of rifle mechanisms. This is achieved due to the ingress of a much smaller volume of powder gases inside the upper receiver and less formation of carbon deposits on the frame with the bolt and the elements of the firing mechanism and, accordingly, gives a lower probability of the rifle jamming.

Also, this design makes it easier to service rifles and increases the interval between mandatory cleaning of weapons, especially when you have limited free time, for example, in combat conditions.

In the SIG Sauer MCX, on which a folding frame stock is installed, the bolt frame design provides for the use of 2 return springs, it is they who provide the reciprocating movement of the bolt frame and smooth out the recoil momentum when firing a rifle.

Rifles are assembled in reverse order.

The barrel is mounted on the SIG Sauer MCX with 2 screws in the chamber area and the barrel can be replaced without completely disassembling the rifle, but in this case, it is imperative to put the rifle on the slide delay to separate the barrel and bolt and remove the forend. On the SIG Sauer 516, the barrel attachment scheme is similar to the AR15.

The SIG Sauer 516 telescopic stock is equipped with a recoil buffer. This design is similar to that of most AR15 rifles and carbines.

The trigger mechanism for the SIG Sauer 516 and SIG Sauer MCX rifles is hammer-type and is entirely made of steel. The trigger travel is smooth with a certain effort. The SIG Sauer 516 has a stroke length of about 4mm and a trigger pull of 3.5kg. On the SIG Sauer MCX, the stroke length of the SK is also about 4mm, and the trigger force on various rifle modifications ranges from 2.99 to 3.9 kg. Reverse trigger travel on both the SIG Sauer 516 and SIG Sauer MCX is about 3mm, which in single fire mode will allow you to shoot at a fairly high rate.

The rifle sights are made of polymer and metal. The front sight has a classic open shape with side lobes, which, in addition to a protective function, create an optical tunnel for ease of aiming. The rear sighting device is a replaceable diopter rear sight. Front sight and rear sight adjustment is easily performed in the field and without the use of special tools.

For this, auxiliary adjusting devices are used, located directly on the rear sight and front sight. When using an optical or collimator sight, the standard sighting devices are folded.
Stores at SIG Sauer 516 and SIG Sauer MCX are box-type, double-row. The capacity of the regular magazine is 30 rounds. Regular stores are not equipped with windows for visual control of the amount of ammunition. Established metal stores.

The rifles left a very positive impression. By combining the popular design and modularity of the AR15 design with the reliability of the gas piston gas valve mechanism, as well as the ability to quickly change the barrel on the MCX rifle, SIG Sauer has created extremely ergonomic and easy-to-use models of modern small arms, and fans of this brand and “Format” AR-15 received the long-awaited version of the army assault rifle, combining elements of the AR-15 and AK.

Do not forget about the rules of safe handling of weapons.


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