When the chips are down, you shouldn't be worrying about your ammunition. PMC agrees completely and responded with their X-Tac line. X-Tac is tried and tested by military and law enforcement professionals around the world. Each round is manufactured to the exacting specifications demanded by operators everywhere. NOTE: While the 5.56x45mm NATO round will fit in a .223 Remington chamber, 5.56 NATO is a military round that runs at higher pressures, and is not recommended for use in .223 Remington chambers.