BCM 16" SS410 upper.
I shot it for a few mags with the factory installed brake. It shot like a laser with the NXS 1-4 and CBC 77gr SMK and ADI 69gr SMK (out to 500 yards). It was obnoxious shooting in a little indoor/outdoor training class.
I took the brake off and screwed on a Smith Vortex G6A3. The brake was TIGHT. Like I thought I was going to crush the barrel blocks or the barrel in the vice and I had to pull out a longer Snap-On wrench to get it off. I installed the Vortex per instructions with hand torque, let it shoot itself tight.
I expected a POI shift. Went to re-zero the gun and spent the next three weeks chasing my tail with poor groups and a wandering POI. Tightened up my mounts, re-locktited everything, was really down on my shooting skills, just having a bad time.
Today, out of curiosity I pulled a brand new A2 flash hider and crush washer and installed it. It took a little over a full revolution of 'crush' to time correctly and I was worried it was too tight.
I popped on a bipod and set a target at 100 yards. Accuracy is back. I shot 4 5 round groups and one 10 round group of ADI 69gr SMK with a 5 gusting 12 mph cross wind and ALL groups were hovering right over 1moa.
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