The Ching Sling is an answer to the question, "how can one have a sling that is both a useful shooting aid and also quick to get in and out of?" The formal shooting sling was a part of US military training for many decades, and is still a staple of long range marksmanship competition. However, it is a complicated process to set up a shooting sling, and in World War Two it proved thoroughly impractical in combat conditions. The idea of using a sling for a support aid was not necessarily a bad one, though.
Eric Ching devised this solution, using three sling points instead of the traditional two. In this system, the center strap and center mounting point are used to create a sling loop around the tricep which can be very quickly positioned. When not in shooting use, though, the middle strap can be slid out of the way and the sling works as a normal carry strap, either muzzle up or muzzle down.
Ching was a student of Jeff Cooper's, and Cooper found the Ching Sling to be an ideal piece of gear to fit onto his scout rifle concept. When Steyr introduced the Scout Rifle they built in partnership with Cooper, the Ching Sling was included as a part of the standard package.
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