It does a hunter no good to head afield with a rifle/load combination that sprays bullets like so many shotgun pellets. In all big-game hunting, the person that can put his or her first shot on the money time after time is the one that will consistently fill a tag.
When it comes to accuracy, the first question we have to answer is, what is acceptable accuracy in a deer hunting cartridge? If you’re a true “gun nut,” you are not satisfied with anything that produces less than minute-of-angle accuracy (defined as three shots that strike the target within one-inch or less of each other at 100 yards). When I started deer hunting back in the 1960s, that kind of accuracy was uncommon, due as much, if not more, to the state of available factory ammunition as rifle construction. Today that has all changed, and finding a deer rifle/load combination that produces acceptable accuracy is not all that uncommon. And while you want the most accurate rifle/load combination you can take to the woods, truth be told, a minute-of-angle rifle isn’t really necessary for most common deer hunting situations. I have shot a lot of game over the years with guns that only grouped 1 ½- 1 ¾-inches. The key was consistency. Those rifles would place the first two shots into the same spot like clockwork.
Most gun writers, including me, at one time or another have said things like, "The .308 is an inherently accurate cartridge." In truth, however, this is very misleading, because it is the rifle itself, plus the care and precision that went into loading a given cartridge, that have the biggest effect on its accuracy. Here’s another little secret: The specifics of the cartridge design itself have little to do with real world accuracy, thus there is probably no such thing as an “inherently accurate” hunting cartridge design. Most any hunting cartridge can be very accurate in a good rifle with precisely loaded ammunition, while producing mediocre accuracy in another rifle with mediocre ammunition.
In general terms, when shot from rifles of equal quality and accuracy, the case capacity determines the inherent accuracy of any given cartridge—not the bore size or shoulder angle or head diameter. To understand this, all you need to do is attend a serious benchrest shooting match, where you’ll see that pretty much all top bench rest cartridges are built on small-capacity cases like the .222 Rem., .22 BR Rem., .22 PPC and 6 mm PPC. That doesn’t mean that very accurate benchrest rifles cannot be built in calibers like .308 Win. and .300 Win. Mag., because they have, but generally speaking, those are not the calibers the top shooters choose.
So then, what’s the most accurate cartridge you can choose for your new deer hunting rifle with factory ammunition? Truly the answer is to buy the best rifle you can afford chambered for a round using bullet diameters between .243 and .300, top it with precision-made scope mounts and quality glass, then head to the range with as many different brands and bullet types of factory ammunition as you can afford to try and shoot them all. Some rifles are friendly, liking lots of different ammo, while some are quite picky, shooting one or two loads well and the rest poorly.