There are legal experts here, I in no way claim to be one. I think it would be a pretty tall order to convince a Judge and Jury that shooting a man 100-400 yards away was self defense. Hard to prove the intention of a man 1/4 mile away.
400 yards is really not very far with a rifle. Any decent rifle will hit a man sized target at 400. I it will not, the barrel is trash, change the barrel. Some good performance calibers wear the barrels a lot faster. The .223 is without a doubt the cheapest to shoot and pretty easy on barrels. Other than the AK round, the .308 is probably the next step up, and easy to find in LOTS of flavors, although more money. Many calibers have some fantastic performance for different things, but I would not want to have to find those calibers in a bad situation.
