WrenTech Industries have started selling a shotgun and Ruger 10/22 rifle variant of their Advantage Tactical Sight. The new sights work the same as the pistol version. To aim you simply line up the rear sight with front sight to create a triangular shape. This apparently allows very quick sight acquisition.
The ATS on a glock and the sight picture.
The Universal Shotgun sight fits any non-ribbed 12 gauge barrel that is 14″ – 20″ long and of .840” to .890” in diameter, which includes most non-ribbed Mossberg and Remington barrels.
Mossberg 500 Shotgun
The Ruger 10/22 variant is only compatible with the aftermarket Tactical Solutions fluted .22 LR barrel. It is designed specifically for .22 steel matches.