The guy asked which is the most accurate action. I just assumed that he meant a bolt action. The stiff ones withoutmagazine cuts, that are made specifically for building long-range target and benchrest rifles, are easier to obtain exceptional accuracy from. Of course, a good barrel is required, as is proper stock bedding. But no repeater action is going to permit the attainment of fine accuracy as well as the heavy single-shot actions that don't have a lot of steel milled off of the receivers.

(ANY kind of an action can be weatherproofed! Even a flintlock......)