Autos can certainly be accurate rifles but when you look at spending equal money on both types of firearms the bolt will almost always be the more accurate of the two.

Things that make the semi less accurate is the venting of the gas to operate the bolt while the bullet is traveling down the bore, the bolt not locking as tightly, the bolt moving before the bullet leaves the bore, triggers are generally not as good with out spendind money, receivers are generally not as strong, moving parts attached to the barrel, etc... etc...