7.62NATO, I had an Aimpoint for a while on a New Englander. It was mounted right over the factory rear sight mounting holes. For me anyway, it was darn near useless for fifteen or twenty minutes at first and last light. Otherwise, I would rate it as OK. I replaced it with a 2X pistol scope mounted in the same place and was much happier, and that forward mounted pistol scope was fast and clear.