This is a SilencerCo Mount known as the Bravo, model AC1415.
SilencerCo Direct Thread Mounts are a simple solution to attach their silencers to any firearm. The Bravo Direct Thread Mount is compatible with the Omega 300" Hybrid 46" and Harvester 338. Compared to the ASR Mount" the Direct Thread Mount shortens the overall length of the suppressor by 3/4". With many thread pitch and caliber options" your silencer is ready to shoot on almost any platform. Bravo accessories are compatible with Omega 300" Hybrid 46" and Harvester 338.
Features:
Compatible with Omega 300, Hybrid 46, and Harvester 338
Shortens suppressor length by ¾"