A lot of deer hunters believe the .223 Rem. is not enough of a cartridge to be called deer ammo. There is some logic behind this. After all, deer are sometimes lost to hits from cartridges as large as the .30-06. Truth be told, those lost deer are more than likely due to bad shooting as opposed to bad or little bullets. Regardless of what cartridge you deer hunt with, your bullet needs to penetrate deep enough to pass through vital organs. It should also expand or deform in a way to maximize the destruction of those organs.
The .223 Rem. is legal for deer hunting in a lot of states, and has proven to be effective when proper bullets are used. The down side to the .223 Rem. is not velocity or bullet diameter; a .243 Win. is no faster, and its bullet is only .02 inches wider in diameter. (That's a difference of less than the thickness of your credit card.) Bullet weight is the .223's weakness. Because most bullets shed weight as they expand and penetrate, bullet expansion combined with weight loss limits penetration. For .22 caliber bullets to be effective on deer, they need to expand wide so they can maximize tissue destruction, but they also need to maintain their weight so they can drive deep.
Bullet makers have addressed this with what some call "premium" bullets for the .223 Rem. Bullets like the Nosler Partition and Barnes TSX, which are loaded by Federal, and one of my favorites, the 62 grain Fusion load, are perfect examples. These bullets will double in diameter when they expand, but lose very little or no weight at all. The result is a bullet that will penetrate as deep as any .30-30 Win. bullet, and often damage more tissue because of the higher velocity.
Velocity is important because a higher velocity means more displaced and damaged tissue. A bullet sort of makes a splash inside the liquid-filled tissues of a deer—like when you throw a rock into a pond. Throw the rock slowly and you get a small splash; throw it faster and the splash is bigger. Muzzle velocities from a .223 Rem. are fast—1,000 fps faster than a .30-30 Win. However, because of the low ballistic coefficient (BC) of .224 caliber bullets, they slow down quickly. (Note: The .223 Rem. actually has a .224-inch diameter.)
To make these premium bullets expand to their maximum diameter for maximum tissue destruction, they need velocity. Ideally, they will have an impact velocity of 2,400 fps or more. This means shots on deer with the .223 Rem. should be limited to about 150 yards. Past that distance, impact velocities will be so slow, expansion and tissue destruction will be limited.
The only viable exception to using these premium bullets with the .223 Rem. is the ammunition from Dynamic Research Technologies (DRT). The bullets DRT uses are made from very, very small copper particles that have been compressed into a solid and inserted inside a thin copper jacket. Because of their profile and internal construction, DRT bullets penetrate several inches of hide, muscle and bone before they begin to react. When they do react, they don't expand—they literally decompress and send miniature copper particles throughout the deer's vitals. The wound cavity created is unmatched by any conventional or premium bullet.
With the DRT bullets, you will not see an exit wound like you will with the Nosler Partition, Barnes TSX or Fusion bullets. However, because of their violent upset and the massive internal damage they cause, you can expect deer to go down fast. For DRT bullets to be the most effective, they need the same level of impact velocity as the premium bullets do when fired from a .223 Rem., so keep shots inside about 150 yards.
If you use the right bullets and shoot straight, the .223 Rem. is a fine deer cartridge out to about 150 yards. The very light recoil of the .223 Rem. also makes it a cartridge most anyone can shoot accurately. And unless you want to lose that deer, accurate shooting is just as important as bullet selection, regardless of what cartridge or bullet you use.