Squires, glad to hear you did so well with your experiments, though what I would say is that how you perform when relaxed with no pressure is a whole different ball-game in competition and this is where the sling can be useful if nothing else for those first few lanes until you're in the groove.
For prone shooters, the sling is all as it provides complete support for the weight of the rifle, for sitting and kneeling for me it provides a steadying influence which I find useful. Obviously the knee is still bearing the weight of the rifle, but the sling allows the left arm to pull the rifle into the position and stop the wavering you can experience especially in the heat of a difficult shot.
I applaud Simon for persevering with the absurdity of permanently having the sling attached to the rifle and slipping his arm in and out of the cuff loop between lanes.
Totally how a single-point sling should not be used and must be a right pain especially in competition.
Just to give you an idea, the sling should be positioned on the upper arm above the muscle which is why gimp coats have that little spade buckle called a keeper, yes it's there to hold the single-point sling in the right position and stop it dropping down to the elbow.
At the other end, you have a metal 'claw' which slips into usually an oval shaped swing swivel which can pivot and allow the sling to attach/detach easily.
Then finally you have a hand-stop, which as it suggests stops the hand getting caught up in the swivel as well as providing a consistent pressure point for the stock to locate against.
That pretty much covers the single-point for both small and full bore in the prone position which we obviously don't use.