These straps are called AMMO straps.
True and original AMMO straps should be made from old AMMUnition bags (made of leather)
These old ammunitions bags used a fastener device consisting on a metallic ball or cone and a leather ribbon with a "tear shaped" notch like showed in your strap.
A true AMMO strap should have the fastener made with the fastener of an original AMMUnition bag.
Your strap obviously is a "copy" just remembering those old ammunition bags.
See below pics:
Hope that helps
ALE