Mechanically a bolt is more accurate, as it locks up the same way each time, and is a stronger action. A semi auto doesn't lock up the same when you just release the bolt by hand. When it is cycling itself after a shot the action slams shut a lot harder, which has a profound affect on accuracy. After the first shot, shot to shot accuracy does become more consistent. A bolt action can also stand a higher pressure, and can't fail to lock up due to dirt and carbons building up in the chamber. If you keep the semi auto clean its typically not an issue, but I have seen some semi auto 22's fail to close. Theoretically the buildup could cause the bolt not to lock on the semi auto, and still fire the round, causing blowback.