The double snap your feeling is present on most nocks to some extent. The reason is when you draw your bow if your not using a loop the angle of the string causes it to become unseated from the throat of the nock. If you didnt have the second set "snaps" if you let the bow down the arrow would fall off the string. If you want to see what I mean snap the arrow on the string and then lift up on the front of the arrow to simulate the string angle at draw. As you lift youll feel the first set disengage and the second set will then be stopping the arrow from falling off the string.