William, the Savage Axis is only capable of handling 223. savagearms.com/content?p=firearms&a=product_summary&s=57233

Up near the muzzle the barrel will be stamped either 556 or 223, if it has the 556 stamp you are good to go with either, if it says 223 only fire 223. They is honestly a greater variety of bullets in 223 anyways, so even with a 223 only barrel you should be able to find ammo to meet your needs.

William, the Savage Axis is Barrel Stamped .223 and 5.56 (higher pressure military loading) would not be recommended. However, for warranty and safety reasons, I would seek advice from the manufacturer and holder of your warranty, Savage Arms Customer Service at (800) 370-0708 Monday through Friday 8:00AM – 5:00PM EST

Negative, the 5.56 round is slightly longer than .223 and shooting 5.56 through it could cause an over pressure situation.