Colin Shadbolt wrote years ago (in 'Australian Outdoors') that Westley Richards put peep sights on .318 magazine rifles intended for shooting lion. He claimed apertures were accepted as the fastest sight beyond 40 yards.

I have put them on four rifles and, with the disc out, find them quicker than a scope and close to that of an express sight. If the rifle fits properly you can pretty much ignore the rear sight and don't have to worry whether you're taking a fine enough bead - as I do with express sights.