6mm Grendel Group Design Project

[StoneHendge]

There is a bigger selection of .223 muzzle devices with 1/2"-28 threads.
Clearances would have to be checked between bullet diameter and ID of muzzle device.
I know you know this but I am only posting this in case there are others that try it. Maybe you have more ideas.

My guess is that whoever made the barrel screwed up. Seems like an odd caliber and configuration for a custom manufacturer to make for stock. I’m sure they’d cut and rethread it for someone who asks. I did have a good visualization of Bugs Bunny handing a rifle with a muzzle device that’s too narrow to Yosemite Sam.