Midwest Industries, Inc. offers quite a few different sling mounting solutions for the AR platform, and shown here are some of their front sling adaptors. They’re manufactured out of 6061aluminum and hard-coat anodized black.
The renewed interest in two-point slings with the introduction of BFG’s VCAS (below) has added to the demand for rail-mounted sling adapters. I’ve always preferred a side-rail mounted adapter instead of the front sight mounted sling swivel (either on the side or at the bottom), as a forward attach point for a 3 point or 2 point sling. For one, the sling doesn’t need to be as long. Additionally, I find it easier to manipulate and manoeuvre the rifle when the forward portion of the sling is attached to the rear or middle of the rail. All the MI adaptors attach to the rail with an allen-head screw.