GUNS Magazine Map SIG Sauer MCX Rattler

Caliber details

The tested .300BLK version of the SIG Rattler PCB feeds supersonic and subsonic shells with comparable ease. The gas system adjusts using nothing bulkier than the tip of a cartridge or even your fingertip if you’re up for it. One setting is for supersonic ammo. The other is for subsonic tri. We had no downtime.

With a SIG SRD762 sound suppressor in place, the gun is ridiculously quiet with subsonic ammo. SIG canisters are built like armored fighting vehicles. They make things from Inconel 718, a nickel-alloy stainless steel widely used on Navy submarines, jet engine thrust reversers, and nuclear reactor core components. The SRD762 is a radical and efficient tubeless design that will outlast you.

The .300BLK cartridge has found a solid niche in civilian and law enforcement applications. There are even a few spooky high-end military organizations allegedly with an operational affinity for the cycle. Jason Imhoff, the guy who dreamed up the .300BLK in the first place, is SIG’s Director of Ammunition Engineering. The real strength of the .300BLK cartridge is that it will perform in standard magazines using standard 5.56mm bolt carrier groups while delivering subsonic and supersonic velocities depending on bullet weight.

Supersonic charges are just fine for hunting white-tailed deer here in the Deep South where I live. Subsonic rounds through a suitable sound suppressor are simply silent. With the Rattler circuit board and some cool accessories from SIG, you can choose your poison.