5.56mm and .223 are close to each other and almost the same. You can fire .223 in 5.56mm guns, but NOT 5.56mm in .223 guns. I've got a Bushmaster XM15-E2S (AR15) and I love it. It's chambered in 5.56mm. If you're looking for hunting, it'll do some smaller game just fine. I've seen it done with deer too, but it's not a preferred caliber; too likely to not stop the deer unless it's a good shot. They make the AR in 6.68mm(?) and that would do fine for deer.

If you're looking to hunt with it, maybe pick up an m44. I've got one and I love it. Kicks like a mule, but quite accurate. It's 7.62mmx54r. Plenty of knockdown power.

Richard <img src="/forums/images/graemlins/patriot.gif" alt="" />