I was going to leave this one alone, but i have to weigh in on the side of common sense and caution. The .223 is IMO, effective, but VERY limited. Ive killed a great many deer and goats with the round, and one shot drops are not unusual but also not common.
Again IMO, you have two choices in loads and placement. You can use the haviest varmint/small game bullets (which are generally a bit tougher then thier lighter counterparts), and be VERY selective of your shots, since penetration will also be very limited. Personally thats the option i use, broad side, standing double lung or heart.
The other option are the much tougher bullets like the x or sirroco. both penetrate well, but you dont get the trauma of the softer bullets. You still need to be able to put the round thru the vitals, but your presentation and angles can be a little worse. My experiance with these bullets are that they dont generally drop anything on the shot, and usually the animals are best treated as arrow hit and given some time to expire.
I have also used a .22LR to very good affect on both body and head shots while doing control work, both at night and durring the day, another person im familiar with but never seen hunt swears by the .17 with FMJs for the same type of work. Again, know your tool, use it well (and within its limits), and you will succede.....on the other hand a little insurance never hurts.