I want to say I seen this sling on a BAR in a photo?
I don't think its any more complicated than the m1907 just sewn up different and with a buckle or 2 on it?
From a little info I found it was going to be a replacement for the m1907 sling just in a cotton web sling material, then the basic web sling came along. You know how it goes just good enough for GI is what GI gets. The "GI web sling" as we know works and is "cheap" to make.