Late last week, the United States Special Operations Command announced they had awarded SIG SAUER a $49 million contract for Suppressed Upper Receiver Groups for the M4A1 weapon.

Here is the first photograph of the SURG in the wild. The SURG components are mounted to a generic AR-style lower receiver.

Based on the SOCOM requirement, SURG includes a 5.56mm NATO upper receiver group (URG) composed of upper receiver, barrel, operating system assembly and bolt/carrier assembly along with a sound suppressor (may be integral with barrel), operators manual and maintenance manual. In addition to the URG itself, candidate systems could include a folding stock if the operating system didn’t require use of the lower receiver extension, buffer and action spring.

As we can see here, SIG went a different direction than most and used an MCX piston driven upper with detachable suppressor and an MCX folding stock. As part of SURG, SOCOM will receive the folding stock and knuckle adapter for use with existing M4A1 lowers. The suppressor is covered with some sort of aramid-based mesh to protect the hand of the operator. When you get to the performance specs below, you’ll understand why this is so significant.

I’m now going to go over some of the requirements for SURG so you can see how SIG (and the other candidates) had to perform to win this solicitation.

SOCOM stipulated that SURG could be no more than 25.5 inches in length but that they preferred a system that was no more than 21.0 inches. The barrel has to be at least 11.5 inches in length and the weapon can’t weigh more than 7.0 pounds, but the preferred weight is just 4.5 pounds. It also needed to be Coyote 498 in color.

The real meat of the requirement is in the suppressor performance. First off, a SURG equipped M4A1 has to be optimized to fire the M855A1 and the MK318 MOD0 / MOD1 cartridges and be able to do so reliably for at least 1200 rounds without lubrication. Obviously, they also didn’t want anything that could vibrate loose. While the suppressor must be rebuildable, only one component of the suppressor has to be serialized but that part had to last the lifetime of an M4A1 lower receiver (125,000 rounds). The rebuildable components need to last at least 15,000 rounds but SOCOM further challenged industry to make them last for 20,000 rounds.

Additionally, a SURG equipped M4A1 shall not exceed 140 dB ten shot average sound pressure level at shooter’s ear during barrel life minimum (15,000 rounds).

In the past I’ve mentioned the so-called SOCOM suppressor torture or stress test. The SURG equipped M4A1 has to withstand at least 6 complete cycles of the firing schedule seen below below using MK318 MOD0 / MOD1 ammunition with SURG allowed cooling to 120°F after each cycle. However, SOCOM was hoping to complete 20 cycles.

The weapon firing MK318 MOD1 for 5 groups of 10 rounds each suppressed, has to average over the 5 groups no more than 1.50 MOA Extreme Spread (ES) beyond the ammunition Lot Acceptance Test (LAT) average ES at 300 yards. Also, it has to maintain a maximum ES Average of 1.50 MOA over LAT using MK318 MOD0 / MOD1 ammunition from 0 to 10,000 rounds fired.

In addition to that stress test, SURG has to prevent operator contact or sustained contact burns from the suppressor (or equivalent) through 1 layer of standard military duty uniform material after firing 210 rounds in 7 minutes at a rate of 1 round every 2 seconds ± 0.2 seconds. A contact burn will be defined as a peak temperature over 160°F in 1 second of contact. A sustained contact burn will be defined as a peak temperature over 160°F in 5 seconds of contact.

These stringent requirements, combining suppression, reliability, accuracy service life, and operator protection were very challenging for industry. It took three tries at bat for the SURG program to finally select a system. In the two earlier attempts, none of the systems could meet all of the program’s objectives. Kudos to SIG for putting together a winning system.