be selective
Pick and choose your shots and your ammo. With the AR/.223 craze in full cry, deer and hogs are getting shot with .223 in large amounts and prove it can be done. But avoid "anything" ammo choice, and any advice to "head shoot" to solve the ammo problem.
Sooner or later, using frangible/varmint slugs, you'll get a shot at a less than ideal angle, or a shot that lands on a big bone, and limits your penetration, or a shot farther than anticipated, that effects placement and performance. Result may be no exit, puny blood trail, failure to reach vitals and an escaped or wounded animal. Lets hope the "anything" advice did not include FMJ for hopefully several obvious reasons.
There was a time when taking deer with a .223 was looked upon as a "stunt", and there are still places where it is not legal, and those who largely condemn the practice even if it is. Experience is proving that the .223 can take deer cleanly, but common sense must prevail, and accept that the cartridge has its limitations with medium to big game, and the right slug can tilt the balance more in our favor for clean kills.
Bamaboy took his first two deer with a .223 bolt rifle, bonded bullets (federal 62 gr tactical/bonded). Under 100 yd shots, broadsided, heavily coached and well practiced, me at his ear, the rifle on a support. Number one was a pass through, double lung, heavy blood trail, the doe went about 75-100 yds with a heavy blood trail. NUmber two, double lung, slightly more quartering angle, deer close and velocity high, no exit wound, and zero blood trail. The doe went about 50 yds, in heavy cover, and waning light, and had we been less than diligent and certain of a hit, the deer may have gone unrecovered. We found the slug under the hide on the off side, after clipping the liver, a classic mushroom. Any heavier rifle would have almost certainly passed through and given us an exit and a better trail. We moved up to 7.62x39 and then .243 and now I have to fight the kid for one of my .308's.
I've seen enough deer taken with a bow and muzzle load roundball, to realize that placement and experience can yield good results no matter what the weapon. But the same discretion used in the former applies to the .223 I do believe.