Much has been made of the difference between .223 ammo and 5.56 NATO ammo. While they look alike, perform alike, they're not alike. Knowledgeable gunnies know the difference. Go to The Gun Zone for a complete discussion, but generally, 5.56mm NATO ammo is loaded to a higher pressure level than .223 Remington, and the military chambering normally has a longer leade than sporting rifles. It's generally considered unsafe to use 5.56 mm ammo in sporting rifles chambered for .223 Remington.
However, my Bushmaster is specifically marked for both ammo types, which indicates to me that it has the longer leade and was proofed for the military ammo. It's perfectly safe to fire the .223 Remington in that rifle.
However, today when we were at the range, I noticed something that I had never noticed before. The boxes of ammo we were issued were marked as 5.56. While I'm sure that Winchester makes a lot of ammo for our military, I had never seen it sold in a commercial box. All military ammo I ever used was packaged in a plain brown cardboard box. Yet, plain as day, I had a box of Winchester ammo marked 5.56 mm.
I thought that was odd enough that it merited its own blog post.