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Sig Sauer MCX Rattler PCB
Sig Sauer MCX Rattler PCB

Sig Sauer MCX Rattler PCB .300 BLK

  • Compact
  • Lightweight
  • Good ergonomics
  • Trouble cycling subsonic ammo without a suppressor
  • Expensive
Editor’s Note:

“Designed for rapid deployment from concealment, the MCX Rattler packs a punch in the .300 BLK configuration. Coming in at 5.1 pounds empty, sporting a 5.5-inch barrel and folded length of 17 inches, the MCX Rattler is definitely compact enough to be carried anywhere.” – Joshua Fox

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Sig Sauer MCX Rattler PCB .300 BLK Specs

Barrel Length
Magazine Capacity
300 AAC Blackout
Overall Length
5.1 lbs

Sig Sauer MCX Rattler PCB .300 BLK Features

30+1 capacity
Free-float M-LOK handguard
Ambidextrous safety and magazine release
Adjustable gas piston
Folding brace
QD sling points

By The Numbers - Sig Sauer MCX Rattler PCB .300 BLK

The 5.5-inch barrel on an AR Pistol isn’t designed to be the most accurate gun in your safe. But it can be very accurate under 50 yards with some proper shooting fundamentals.
Supersonic ammo works great. We encountered multiple failures when trying to shoot subsonic ammo unsuppressed.
Most standard AR-15 modifications will work here, just be mindful of vertical grips and stocks since these are considered pistols.
The brace can be a awkward to shoulder, but ambi controls and a comfortable pistol grip help make the gun feel good in the hand.

Hands-on Reviews and Related Posts

Sig Sauer MCX Rattler PCB .300 BLK Variations & Comparables

Sig Sauer MCX Spear

Sig Sauer MCX Spear


The Sig Sauer MCX Spear is a new battle rifle from Sig Sauer based on the XM7 design submitted for the U.S. Army’s Next Gen Squad Weapons System. Chambered in 7.62x51mm, the MCX Spear will eventually see other caliber models added to the lineup, like the 6.5 Creedmoor and .277 Fury. The MCX Spear is a feature-rich rifle with a comfortable grip, adjustable gas system, and a fully ambidextrous setup. The Sig Sauer MCX Spear is a great choice for anyone looking for a modern, reliable, and versatile battle rifle.

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Daniel Defense DDM4ISR

Daniel Defense DDM4ISR


“The DDM4ISR is a .300 BLK integrally suppressed rifle from Daniel Defense. It sports a 9 inch cold-hammer-forged barrel with an overall length of 16-inches. This gun features a Keymod handguard and handles just about as smoothly in a shoot house as it does out on the range. We had no problems whatsoever during our testing. This rifle loaded, fired, and ejected perfectly. The grip angle may feel odd to some, but overall it’s great once you get used to it.” – John C.

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The LWRC DI is one of the more affordable options for users who are looking for a fully ambidextrous high-end AR-15. These guns are duty ready and feature-rich at a competitive price point.

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Sig Sauer MCX Rattler PCB .300 BLK Upgrades & Accessories

final verdict

“The MCX Rattler is still an absolutely fantastic gun when shooting supersonic ammo. It is small, and concealable in any standard backpack. Not to mention, it packs a punch with a 30-round magazine that can reach out to a couple of hundred yards. Plus, it just looks really cool. Just make sure you pay attention to what ammunition you purchase and feed it if you are not running it suppressed.” – Joshua Fox

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