I do not have a head and shoulder gauge. I just tried a sized case only in my chamber and it is a tight fit also. The neck diameters between the dummy round and the factory round are almost identical with the dummy round being the smaller diameter of the two. I just remeasured the 2 and the only difference seems to be the angle of the shoulder on the old Remington case (dummy round). Also when I sized them I bottomed them out so it's not like I am not getting a full size on them.