The right caliber has enough power for the job, recoil you can shoot well and ammo you can find. Here are the rounds most shooters choose from.

Small and fast
The .22 LR is the king of cheap practice. The .223 Remington and 5.56 NATO run in AR-15s and are great for varmints and targets. More on rimfire in Rimfire and Air Rifles.
Deer and medium game
The .243 Winchester, 6.5 Creedmoor, .308 Winchester and .30-06 Springfield cover nearly every deer hunt in North America. The 6.5 Creedmoor and .308 also dominate long-range target shooting.
Big game and big bores
Magnums like the .300 Win Mag reach out for elk and bigger game. Lever gun rounds like the .45-70 hit hard at moderate range.

Bullet weight
Most calibers come in a range of bullet weights. Lighter bullets fly flatter, heavier bullets carry more energy and penetrate deeper. Match the bullet to the game.

Watch and Learn
Videos from the Gun Websites YouTube channel.
Ready to buy ammo? See Ammo Buyers Guide.com for prices and loads.