All non custom rifle makers know they have to produce rifles of GOOD accuracy. They know "marginal" or "so-so" is not good enough. They know hunters EXPECT a solid gun, complete with a GOOD trigger and MOA accuracy. SO, IMHO, the make & caliber of a rifle is not the main factor.
Optics. It has already been said; "Spend more $$ on optics then on the gun". Spend as much money on optics as you can afford. And then save up (or borrow or beg) and upgrade when you can. There is a huge difference in a $70 Simmons and a $800 Zeiss Conquest.
Shooter Skill, Experience, Confidence.
The most accurate rig in the world will be only "marginal" in the hands of a shooter that lacks form, lacks confidence or flinches. Iv seen MANY hunters/shooters have a NICE gun/optics set up and shoot it horribly, and "someone else" take it and shoot the eye of a fly at 300 yards. Even a rig with marginal accuracy can be shot with better by a shooter with superior skills then someone inferior skills. Superior skills comes with practice, practice, practice (experience), and the more practice you have the more familiar you become with your rig which builds confidence. You got to shoot the thing, a lot!
A lot of hunters/shooters got for a "macho" caliber like a .300Mag or 7mmMag, and shoot it with marginal accuracy. You have to, MUST, be 100% comfortable with the gun you shoot; bolt, pump, auto or single shooter.
Good Short Read on Rifle Accuracy And Another 
