A firearm mounting plate assembly is provided. The firearm mounting plate assembly includes a firearm slide with a first side, a second side, and a top side. A recess defined by a first slide wall and a recess base surface is disposed on the firearm slide top side. The recess includes a rib. The firearm mounting plate assembly includes a mounting plate with a top surface, a bottom surface, a front side, and a rear side. The mounting plate includes one or more bosses. The mounting plate is configured to secure within the recess of the firearm slide.