Couple of points here. In the original post,that was a bolt rifle with a traditional stock,a traditional scope,and a traditional leather sling. No way in hell can you sling that thing under the coat and hope to hide it or be able to use it quickly.
@sneakypete Yeah, that's right - I ain't commenting on that rig, but that a mountain sling would do what that don't... Not meaning to call you out, jussayin.
The second point is personal. I don't consider crap like AK's to be rifles. At best,they are carbines.
Right - I have a mountain sling on most everything I own, but the single point stuff is for carbines. I run that rig on my long guns too, but more for the ability to backpack the rifle, than for center forward single point.
Back when I was walking around in the woods with stuff like that,I just used a piece of canvas web from some forgotten piece of equipment for a sling. Tied one end towards the muzzle,the other end around the butt stock,and slung it over my neck with the firearm pretty much level without me holding it. Wasn't fancy,but this was in the 60's,and the system worked well.
Come to think of it,it may have been a strap from a canvas rifle bag we used when parachuting from airplanes. Or maybe not. It's been a long time and it was something I just did without giving it much thought other than "I need to be able to keep the rifle level at waist level and to be able to take my hands off of it so I can eat rice while walking,look at a compass,etc,etc,etc,and yet be instantly ready to shoot it. Yeah,that will work!"
Yeah - not the same, but sorta. If I am in the woods, I am packing a 45/70 and it is on a forward center single point. Same sort of thing for the same reason why. The rifle has to be at the ready, mostly at all times. It's mighty nice to be able to tuck it under my arm (barrel down) if I am stopped to do something I need my hands for... It is still very much accessible, far more than a shouldered sling would be.
It don't travel that way of course. If I come up out of the brush into meadows, or walking a ridge, it is an easy thing to convert it to 2 point and put it on my back.
That's why I like it. Because it is so versatile.