I know all about the higher pressures of 5.56x45mm in the AR-15 platform. A rifle chambered for ".223" should NOT have 5.56mm rounds fired in them because the chamber might go kaBOOM. Whereas "5.56x45mm" chambering means it can handle both rounds. Is this the same in the .308/7.62x51mm world? I just cannot tell if they are the same or different. I can't tell if one (7.62mm) means I can use both and the other (.308) means I can only use one (like the .223/5.56mm world). I think my question is clear. Please help!!