With a very similar external casing of a standard NATO 5.56 x 45mm cartridge jacket, but shortened and married to a .30-caliber bullet rather than being necked down to .22 caliber, the 300 BLK is considered to be better suited for suppressed firing while also providing similar muzzle velocity to the M4A1 when fitted with a more conventional 14.5-inch barrel. With a similar overall length to the 5.56 X 45mm round, the 300 BLK can also fit into existing 5.56 magazines, and a relatively simple change of barrels allows many 5.56-chambered weapons to fire the 300 BLK.

It is precisely these specifications that have promoted 300 BLK’s suitability across the special operations community, defense sources explained to Special Operations Outlook.

Having first disclosed the requirement to the market on March 9, 2017, USSOCOM awarded SiG Sauer a contract on Feb. 1, 2018, worth an undisclosed sum, to supply a total of 10 PDW conversion kits to NSWC Crane Warfare Center, Indiana, ahead of an evaluation with a Joint Acquisition Task Force (JATF).

According to a statement from the U.S. Army Contracting Command, published on the Federal Business Opportunities website, SiG Sauer emerged as the only OEM to offer up a viable solution to the PDW requirement.

“SiG Sauer was the only company identified through market research that could provide the necessary … PDW Parts and Kits which met the Government’s requirements for a Commercial off the shelf conversion kit for the M4A1 to create a … PDW,” the statement reads.

SiG Sauer’s conversion kit is based on its MCX Rattler carbine, which was first unveiled to the market at the SHOT Show in Las Vegas in January 2018.

Discussing the conversion kit with Special Operations Outlook, USSOCOM sources explained how the upgrade could be achieved through a simple replacement of weapon stock and upper receiver, which includes a 5.5-inch barrel in a 300 BLK configuration, satisfying SOF requirements for a smaller form factor for increased maneuverability in confined spaces.

Additional USSOCOM requirements called for a PDW comprising no more than 5.5 pounds in total weight, with weapon profile measuring no more than 26 inches in length, official documents confirmed. The 300 BLK conversion kit must also satisfy accuracy demands of 2 minutes of angle at a range of 100 yards.

SiG Sauer was unable to comment on additional details. However, company officials confirmed that each conversion kit supplied to the NSWC Crane Warfare Center would not only feature the MCX PDW 300 BLK upper receiver group, complete with 5.5-inch barrel, but also an MCX barrel in 5.56 x 45mm caliber; SiG Sauer’s SRD 7.62mm suppressor with handguard (to avoid damage to the supporting hand when operating the weapon); a variety of weapon stocks in folding, telescoped, and skeleton configurations; quick detachment sling adaptor; set of 10 magazines capable of housing 300 BLK ammunition; and optical weapon sights including the Wilcox Boss 300 BLK and SiG Sauer’s own Juliet X4 magnification sight.

Each conversion kit will also be delivered with a polymer rifle case, capable of housing both 5.56 x 45mm and 300 BLK conversion kits.

Speaking to Special Operations Outlook, one operator from an undisclosed NATO SOF unit in Europe described how such a conversion kit would allow teams to deploy to forward operating bases with a single rifle case featuring immediate accessibility to both 5.56 x 45mm and 300 BLK weapon systems.

Upon receiving mission orders, an operator could then rapidly reconfigure his/her personal weapon system in accordance with designated rules of engagement or threat assessment, dependent upon lethality levels required.

According to USSOCOM officials, deliveries of the 10 conversion kits will be completed by the end of the first half of 2018, with a JATF conducting a follow-on evaluation program to assess its suitability for frontline service.

Meanwhile, USSOCOM components are also considering additional “alternative” caliber types beyond 300 BLK in order to satisfy emerging operational requirements concerning the effectiveness of legacy ammunition armor penetration levels against near-peer adversaries.

According to one SOF source, coalition special operations units operating 5.56 x 45mm-caliber carbines have yet to witness any significant problems with this particular ammunition type.

“[5.56mm] is doing what it is supposed to do, but looking at the capability of our peers, it’s worrying,” the source warned.

Elsewhere, undisclosed special operations users in the UK are also scheduled to receive initial deliveries of 300 BLK supersonic and subsonic ammunition as part of a Ministry of Defense (MOD) solicitation published on July 12, 2017.

Deliveries are expected to begin in April 2019 ahead of an evaluation program, defense sources confirmed to Special Operations Outlook, with the first procurement tranche being relied upon for “operational and training ammunition.”

Evaluation of 300 BLK ammunition will concentrate on battlefield and terminal effects; climatic and environmental characteristics; munition sensitivity; system and design safety; interoperability with other carbines; human factors; deployability; sustainment; and capability resiliency and reliability. The MOD was unable to provide Special Operations Outlook with additional details regarding the customer.

Germany’s army special operations command (KSK) is also considering the procurement of MCX carbines in 300 BLK, with sources suggesting force elements had already received an undisclosed number of systems for evaluation.

However, the wider proliferation of 300 BLK carbines across European SOF remains unlikely in the near future, with both German and Dutch SOF units selecting a next-generation carbine in 5.56 x 45mm caliber.