I use Fiocchi 50gr v-max in my Bushmaster Predator AR15 for Rabbit Hunting and they are excellent. I have also used Hornady 55gr v-max but the fiocchi are heaps cheaper and their doesn't seem to be any difference in accuracy.
I have a Bushmaster Predator with a Leupold Mark II 6-18 x 40 Scope. AR-15's are very hard to get in New Zealand but are awesome for long range rabbit shooting. We have more rabbits than grass so the AR-15 gets a good work out.