I'll add to this thread over the next few hours and days in the OP and in the text, co check back for updates.

First, a very good overview of why a shooting sling can be useful, and some very modern/quick-to-use versions: https://survivalblog.com/ching-and-rhodesian-slings-by-a-l/

Another excellent reference, with pix and tutorials, is this Site:http://artoftherifle.com/reference-section.  Scroll down to the sling section, but the whole site is GREAT.  The blogger, Todd, also makes slings, and they are well thought-of.

This is an excellent two-point nylon sling that mimics the 3-point Ching sling.  It gives the same shooting accuracy benefits, but does not require the user to install a third sling mounting point.  A good, inexpensive way to investigate a modern shooting sling.  http://www.thewilderness.com/langlois-rhodesian-sling/.  Apparently, this sling is patterned after the leather slings offered by Andy Langlois, the head guy at www.scoutrifle.org.

While I already have a 3-point Wilderness Ching sling, mounted via QD swivels on my Ruger GSR, I plan to buy a Rhodesian sling from Wilderness for experimental use on other rifles whose stocks I do not wish to modify.  The construction and materials are first-class.

Per his latest blog post, not only is he soon to discontinue his blogging, but also sling making once materials run out.

Good news!

Added content to first post.

If you haven't visited this site, may I suggest you do so?  It's pretty good: Art Of The Rifle.

The Blog author also makes slings, FWIW.

The Rhodesian sling would be perfect for Rifles set up with two, conventional sling points, giving 99% of a true 3-point Ching sling, but much easier to install.  Added benefit is less interference with a longer magazine.  I've used the nylon version of the Rhodesian sling, made by The Wilderness, as well as their Ching sling.  It's an excellent sling for shooting and carrying.