As long as the diameter of the barrel and the gas block are the same. If diameter of 300 blk barrel is the same as the diameter of 5.56mm at the gas block then yes the gas block will work.
As long as the diameter of the barrel and the gas block are the same. If diameter of 300 blk barrel is the same as the diameter of 5.56mm at the gas block then yes the gas block will work.