I use the Australian military sling since my rifle can be carried forward for fast draw off the line from either side of the body,,, or used like a regular sling...
It doesn't mater if the barrel is up or down since the drop loop slips off the gun stock fast...
The adjustment buckle is awesome since it fits the hand good that allows for fast adjustments of tension,,, I sewed marker hash marks of White,,, Silver,,, Gray for each shooting positions of Standing,,, Kneeling/Sitting,,, Prone into the sling where the buckle is...
Don't forget to sew a button on the back sleeve of your shooting jacket that serves as a marker point to let you know that the sling is in the same spot every time...
Once the sling wedges into the button your good to go...
If you get a chance to read the artical from German,,, you'll see what we're doing,,, sling operation is more than just planting the rifle,,, 90% of it is finding that fit,,, how to master it,,, and keep it the same for all 4 shooting positions even though each of them require different tensions...
German's articals will get you up to speed fore sure...
Good shooting all...