Hey this is probably a dumb question from a AR newbie but doesn't hurt to ask so I get my stuff straight and blow my barrel up in my face. So I bought a Stag Arms Model 2 http://www.stagarms.com/product_info.php?products_id=206 yet to shoot it planing on it sat. Anyways I have been searching for ammo for it I know it will shoot .223 but how about this stuff? http://www.federalpremium.com/resources/xm193.aspx I bought a few boxes of the XM193F 5.56mm M193 Ball, is it safe to shoot out of my model 2? Only reason I ask is it says this right on the ammo website... WARNING: For use in standard 5.56 mm chambers. Do not use in non-standard 5.56 chambers. Now my barrel says 5,56 but what is a non standard 5.56? Am I missing something? Are there 2 different types of 5.56 or something? Sorry if this is a completely dumb question but rather confirm than be sorry down the line.