Use a 20" barrel to get decent velocity out of the 60 grain Nosler Partition. Another usefull bullet is the Hornady 60 grain soft point. I've seen either of these kill deer successfully.
It's not that the 223 won't kill a deer, it's just that there are so many other cartridges that are so much better at the job.
My kids have killed a lot of deer with the 223 but I was always sitting beside them with a REAL GUN to finish the job if needed. I also closely controlled the actual shot and most of the time, the animal was broadside in the open with a considerable distance from cover.
I can only say that it's not IF you screw up and lose a deer it's HOW LONG until it happens.