I started hunting with a .223 just to see how well it performed for myself. started with 60gr Nosler Partitions out of a 20" 1-7 twist barrel. Chest shots worked about like the usual .308 rounds. Nothing moved far after being hit, 50yds at most. Ok, then.
Then transitioned to a 55gr Sierra out of a 1-12"twist 20" barrel. Ummm, WOW! Best deer stopper ever! Nothing hit in the chest out to 100yds has taken another step. Boomflop. Often breaks multiple ribs on the entry side. Usually penetrates clean through, but if the jacket separates it has been found stuck on the far side ribs, nicely expanded, BTW. Cores always go through.
Went a little far forward on this buck and missed the chest cavity at what turned out to be ~150yds. He still didn't go far.
circa 2008
Having been well pleased with the 20" barreled rifles' performances, I have since tested some 16" rifle/load combos. 1-7 twist is all I have, so have been reluctant to use the 55gr bullet in them. But Partitions are still fine. As well, the factory 64 Winchester PP load. Again, about like using a .308. Broke all sorts of shoulder bones at entry with that bullet on one smallish deer, but penetration was still good enough to exit the animal.
Shoulder bone frags circa 2010, 64gr WW PP
Most recent example, made a rearward to forward shot with the "ol' favorite" 55gr/20". Not a big deer this time but broke ribs on the near side and shattered the far upper front leg bone near the shoulder joint! Bullet exited. Deer went nowhere...
Exit wound side:
from 2012
Anymore the first thing I'll pick to take to the woods is a 20" barreled AR with those 55gr bullets. Have put together a lighter upper for this year. No iron sights this time, just a tiny ACOG. (I hunt on the ground 95% of the time. No stands, just creeping about or sitting. No beanfields.)
If you can put an appropriately constructed bullet in the chest cavity at distances less than 200yards, then you should have no problem taking deer..