on private land, you can take them with whatever you want. Quite a few have fallen to .357 revolvers. If all I had was an AR-15, tho, I'd be using a braced firing position and aiming carefully for the brain, preferably from a tree stand, using good softpoints, like the 60 gr Nosler Partition. Put enough 223 fmj's into his chest, he'll die in a few minutes, from blood loss and lack of lung function. With enough holes in the chest-wall, a pneumo thorax condition will be inevitable, collapsing the lungs. If a lung is hit, the animal coughs up blood, aspirates it into the other lung, and drowns in its own blood.