Mikey speaks no lie... states differ so widely on what constitutes a legal firearm for the hunting of big game that there are almost no general rules that can be inferred. If you are in Texas, you can use anything that isn't full-auto or .22 rimfire. Hence, in Texas, an AR-15 in .223 is perfectly legal. However, in Oklahoma, big game cartridges must be at least 24 caliber, so .223 is out. You should check out the "Handgun hunting laws" thread in this forum just to see how much laws can vary.