Gunsmithing Crown Damage

I couldn't tell any of you why, but the issue seems to have been in the gas block and/or gas tube. I changed the block and tube to a JP adjustable and replaced the tube while I was at it. Gun is back to shooting nice tight groups. I reinstalled the old block and tube to confirm and that is for sure what the issue was. Interesting part, I put the old block and tube on a different rifle and it shot fine. For whatever reason it did not like the mk12. Anyways, thank you to everyone who helped. I'm glad I've got the gun shooting again.
Was the gas block making contact with the rail or any mlok accessories? That has happened to me on a smaller diameter rail.