Small-bore cartridges are popular with hunters because they recoil gently and shoot flat. They are not all equally suited to game, though, and the bullet matters as much as the cartridge name.
Check the rules first
Some states set minimum caliber or energy rules for big game, and some require non-lead bullets. Read your state's regulations before deciding that a 6mm is enough for a particular animal.
Cartridges with a hunting record
The 6.5x55 has a long one. In Sweden it is a standard moose cartridge, usually loaded with a heavy soft-point bullet, and its loads are at 6.5x55 ammo for sale.
The 6.5 Creedmoor, at 6.5 creedmoor ammo, is a target cartridge that became a deer rifle thanks to modern bullets. The 6.5 PRC, at 6.5 prc hollow point ammo, adds reach. Both want a hunting bullet, not a match bullet, because a hollow-point match bullet is built for accuracy rather than reliable expansion.
Weatherby's 6.5-300 is a flat-shooting magnum for long shots at deer-sized and larger game, and its hunting loads are at 6.5-300 weatherby magnum hunting ammo.
Cartridges that suit smaller jobs
The 6mm BR is a benchrest cartridge, and 69-grain loads such as those at 6mm br 69 grain ammo are target and varmint bullets, not deer bullets.
The 6mm ARC, at hornady 6mm arc ammo, includes polymer-tip loads. So does the 6mm GT, at 6mm gt polymer tip ammo.
A bullet designed for hunting can take a deer-sized animal at modest range, but a varmint or match bullet cannot be counted on to. Norma's 6mm XC, at norma 6mm xc ammo, is loaded with match-style bullets, so read the bullet description before hunting with it.
Old and AR-sized rounds
The 6.5 Carcano, at 6.5 carcano ammo for sale, is a military cartridge whose soft-point loads are sold to owners of old Italian rifles, and its round-nose bullet is a slow, heavy one. The 6.5 Grendel, at 6.5 grendel 120 grain ammo, sits in the middle: 120-grain loads work for deer at moderate distances from an AR-style rifle.
Game regulations differ by state and species. Confirm the minimum caliber, bullet and energy rules that apply to your hunt, and confirm current stock and state shipping restrictions before ordering.