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Sig Sauer® MPX SBR

By Thomas Murphy

The SIG MPX Short Barrel Rifle (SBR) is based on the SIG MPX gas-operated submachine gun manufactured by SIG SAUER. In the 1970s, Schweizerische Industrie Gesellschraft (SIG) purchased both Hammerli and J.P. Sauer and Sonn and was reborn as SIG SAUER. There are now two SIG SAUER companies, one in New Hampshire, USA, and the other in Ekenforde, Germany.

In January 1985, SIGARMS went into business in Tyson’s Corner, Virginia where the P220 and P230 handguns were imported from Germany. In 2007, SIGARMS underwent a name change to SIG SAUER Inc. The company’s fortunes had been on a downhill run since 2004, with less than 140 employees. CEO Roy Cohen added firearms based on the AR-15 platform, and the company grew exponentially up to 2016 when there were over 1,000 employees producing over 43,000 firearms per year. Current production is based in Exeter, NH.

In 2013, the MPX submachine gun was introduced. It fires from a fully closed rotating bolt and piston assembly. This was done primarily for safety and reliability reasons. Rate of fire is right at 850 rounds per minute, which is rapid, but fully controllable due to the low recoil of the 9mm pistol round. Second round target acquisition is quite fast.

The second generation MPX was redesigned to be converted to shoot 9mm, .357 SIG or .40S&W. SIG calls the system Multi-Cal, however, right now, the only chambering available is the 9mm. The MPX can be fitted with carbon steel barrels in lengths from 4.5 to 16 inches. The MPX is only available to military or law enforcement personnel.

The gas operating system is designed to prevent liquid or dirt from entering the chamber which could cause a malfunction. The closed bolt also makes for better operation with a suppressor. Instead of the bolt slamming back as the gun is fired, there is just enough delay (slight) to allow gas pressure to drop, therefore reducing the sound signature. When fired with subsonic ammunition, the MPX sounds like a standard velocity .22 Long Rifle.

In a side view, the MPX resembles a cross between an H&K MP5A3...

This article first appeared in Small Arms Review V22N4 (April 2018)
and was posted online on February 23, 2018

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