223 Rem. They encouraged CCI (tougher primers) for all loads used in any firearm that has a cost-free floating firing pin since the AR does. Other smart, they stated, it matters little or no and all main brand names will ignite concerning the same. Or, acquire it to the gunsmith https://simonghuur.blogpayz.com/31905981/the-definitive-guide-to-federal-champion-210-large-rifle-primers