I have 2x Knights Armament 1/2x28 threaded QDC 3 prong flash hiders. These are take offs from factory KAC rifles. Neither have any rounds on them outside of what was shot at the factory. I just couldn't find any KAC QDC cans, so I went with sandmans, so switching these out for key-mo mounts. $80/each shipped.
I have 1x Thunder beast SR muzzle brake threaded 5/8x24. This one has some rounds through it, but it's in good shape.