This is a CMMG Magazine known as the 350 Legend chambered in 350 Legend, model 35AFC19.
This CMMG Magazine is a standard factory replacement magazine that is designed for use with AR15's chambered in .350 Legend. It features a stainless steel body and holds 10 rounds of .350 Legend ammunition.
Features:
Stainless Steel Body
10-Round Capacity
Fits AR15 (.350 Legend Caliber)
Anti-Tilt Follower