The late great Bob Milek really liked the 6mm-.223 on every thing from varmints up through large bodied Mule deer. He shot many pronghorn, whitetail, & Mule deer - many of them at extended ranges- with this round. One of his favorite bullets for deer, when using the 6mm-.223, was the 80 gr. Speer Spitzer. He recommended a 14-15" barrel w/a 1-10" twist.
I say get one, develope a good accurate load, and go hunting!
Good luck, Del