Just picked up a Savage rifle in .308 Never owned or shot that caliber before. Is .308 and 7.62x51mm NATO interchangeable? I know it will fire, but are there any issues you can have like with using .223 and 5.56mm in certain AR pattern rifles? I heard that the .308 and 7.62x51mm are necked slightly differently, but it does not matter. Appreciate any input. I found some surplus 7.62x51mm NATO for a great price, but wanted to know exactly before I purchased it. Thanks ahead of time!