OK so I popped for a new AR15. 16" barrel, 1 in 7 twist. Bought it primarily as a range toy but what's the best heavy weight ammo for self defense purposes? Please keep in mind that I'm an old fart whose definition of an assault rifle is a 1894 marlin in 44mag. Doubt I'll ever use it on anything but targets, might come in handy for skunks.