Robert, unfortunately the Holosun HS407K won't fit the shield plus without modification or an adapter. The shield plus uses the RSMc footprint, so does the HS407K but slightly modified. It only utilizes a 2 post (front) configuration. Some slides that are milled for RSMc footprint have a 4 post which prevents you from direct mounting without either having to modify the gun, or use an adapter plate (S&W Shield Plus has the 4 post configuration. Sorry but hope this helps.