Should the end of the QD sling with the retaining ring be placed on the straight gate Karabiner, i.e. the one that is clipped into the gear, or on the bent gate, i.e. the one the rope is clipped into?
In reply to Skip: The retainer should go on the crab that is going to have the rope running through it.It isn't essential but it helps to keep it from moving while you're trying to clip it.
I agree with JLS. The retaining loop is to stop the karabiner from rotating so you don't get cross-gate loading. The weight of the sling and the bottom krab is enough to hold the top krab in place.