Hunting will get a lot more interesting next month when PSE releases their TAC-15 crossbow. It mounts directly on a AR-15 rifle, allowing you to swap between both weapons with minimal tinkering.
Why would you need a crossbow when you are already holding an AR-15? I cannot envision a scenario where it makes sense—unless you are invited to some island beyond the bounds of law where men are hunted for sport. You don't want to make it too easy, so you hunt with the crossbow. Then again, we are talking about the most dangerous game of all here, so you have the high-powered rifle as a backup. Speaking of backups, you might want to add the G.R.A.D. .22-cal knife gun to your double-kill arsenal just in case. Hit the following link to see a video of the TAC-15 in action. [YouTube and PSE via BBG]