The Rattler’s specialized upper receiver is designed to be compact, meeting SOCOM requirements. Barrel length is 5.5 inches using a 1:5 twist rate optimized for heavy bullets. The adjustable gas block facilitates use with both super-and sub-sonic ammunition, and it runs flawlessly when suppressed. Configured as a pistol using the telescoping brace, the overall length is 19 inches collapsed (unsuppressed) and 23 inches extended. The 5-inch M-Lok hand guard provides just enough space for needed accessories and a solid grip, and can be removed in seconds without tools.

The MCX Rattler lower includes an ambidextrous safety and magazine release. Bolt release is oversized making it easy to lock the action to the rear using the ambidextrous charging handle. The pistol grip is a Sig Sauer, featuring a more vertical and slim profile than the standard SIG MCX grip, and the rear face of the lower receiver includes a Picatinny rail mount, making it simple and fast to change braces or stocks. Sling attachments are placed on either side of the hand guard and both sides of the receiver at the rear. 

Possibly the most useful short-barreled .300 BLK platform available today, the Rattler is easy to shoot well, and ours proved 100-percent reliable both suppressed and unsuppressed.

A Sig Sauer Electro Optics Romeo 4T was used for primary sighting during testing. Built to withstand just about anything, it uses solar as well as battery power, yielding a 100,000 hour battery life. MOTAC (Motion Activated Illumination) turns on with movement saving battery life.

Accuracy with the Rattler has always been impressive given its compact size. Zeroing the Romeo 4T at 50 yards with supersonic ammunition, its accuracy was tested using the Juliet 4-power magnifier. Typical groups at this range were in the 1- to 1.5-inch range. The best group, as one might expect, came from Sig Sauer’s 125 grain Elite Match OTM at just under an inch. All match ammunition, most using 125-grain bullets, produced similar accuracy. Moving to subsonics, Sig Sauer’s 220-grain took the day for accuracy with a similar sized group at 25 yards. Reliability with this Rattler is excellent, with well over 2,000 rounds to date.

The best 50-yard 5-shot group came from Sig Sauer’s own 125-grain Elite Match OTM and measured out at an impressive sub-one-inch.

As a pistol, the Rattler fits well into vehicle and home defense applications, so much of my time was spent in and around my Toyota FJ Cruiser. Adding the suppressor makes it a tad more difficult to work in tight spaces, but it remains manageable. Remove the suppressor and things get really compact—the real sweet spot with this pistol. It handily fits in a brief cases and non-tactical looking packs I own. All told Sig Sauer’s Rattler is one of the most useful short-barreled 300 BLK firearms available today. Designed from the ground up to work in this exact configuration it is not some conglomeration of parts. If you are looking for a compact 300 BLK pistol or SBR Sig’s 2018 On Target Editors’ Choice Award winning Rattler needs to be near the top of your list! Contact Sig Sauer; Tel.: (603) 610-3000; Web:


Caliber/Gauge: 300 BLK

Receiver Set: Sig Sauer MCX Virtus

Barrel: 5.5 inches 

OA Length: 19 Inches (collapsed) 23 inches extended. 

Weight: 8 pounds, 13 ounces (with suppressor and RT4)

Sights: Flat Top / Accepts rail mounted sights and optics.

Stocks/Grips: Sig Sauer Rattler hand guard, Sig Sauer pistol grip

Action: Semi-Automatic / Rotating Bolt / Short Stroke Piston

Finish: Cerakote

Capacity: Accepts AR-15 based 5.56mm or 300 BLK magazines

Price: $2,727