I no longer own a rifle in .223 Remington and have only owned three -a Mini-14, a Contender Carbine, and a Handi-Rifle.
I used the Contender Carbine when backpacking in to the Ventana Wilderness and Dick Smith Wilderness in the Los Padres National Forest during California's "A" Zone deer season. The rifle was the lightest stainless steel model I could find, and its form factor worked well with backpacking, being compact and fairly flat-sided. The blacktailed deer I pursued with it were small -I never shot one over 100 lbs on the hoof. The ranges were fairly close, too, with a 150 yard shot being a long one. I'd backpack in and stay out for 7 to 14 days. I would see lots of deer, most of the time, but only shot when I was a certain as I could possibly be of a clean, quick kill. I wasn't shooting at deer that were being chased around by a passle of hunters, either. Under that paradigm, the rifle and cartridge worked as well as anything else would, and I filled my deer tag with it every season that I took the rifle out over a 20 year span -so, somewhere around 15 deer fell to it. I initially used the WW 64 grain PowerPoint factory load. It shot well out of my rifle and I never had any complaints about the terminal performance.
I also hunted the later inland seasons in California and Utah and Colorado during that time. Inland hunts were for larger mule deer, where ranges might be longer, and on National Forest or BLM lands not necessiarily Designated Wilderness areas, so I was also hunting more "pressured" animals than I commonly encountered in blacktail hunting. The .223 stayed in the safe for that. I probably could have made it work if it was all I had for California mule deer hunts, but it would have been grossly unsuitable for the hunting I did in Utah and Colorado, as elk might be on the agenda, too. So I tended to use a .30-30 and a .270 or .30-'06 or .300 Weatherby Magnum for those hunts.
When I moved to Oklahoma, a lot of my guns remained in storage in California, and I had an opportunity to get a deal on a Handi-Rifle in .223, which I used to kill a whitetail doe weighing about 90 pounds on the hoof, and a buck weighing about 140 -both shots well under 150 yards. When I got my guns home, I sold off the Handi-Rifle to finance upgrades and overhaul to my .30-30.
I know from first hand, practical experience that a Contender Carbine in .223 Remington can be pressed into service as a "deer rifle" and since I did that same thing for many years, it would be hypocritical of me to say that it couldn't, since I not only used it, but used it successfully but under a farily narrow set of circumstances on smallish deer.
JP