It doesn't effect the intrinsic accuracy of a rifle but will affect the rifle/man interface and that is part and parcel of the useability of the rifle. This is the useable accuracy of a rifle. A correctly fitted rifle, in a very general sense, will allow the shooters trigger hand elbow to be at a 90 degree angle with the hand on the grip(in a firing position) and the butt to the shoulder. This is really quite general and many things can alter this length, clothing, butt stock pitch, caster/chamber, cast off, just to name a few. In an ordinary stock a measurement allowing that angle on the shooters strong side arm will be a good measurement. if the rifle is used in colder weather tighten the angle up and bit and allow a shorter tock for the use of heavier clothing.