This is a replacement base plate for a Smith & Wesson M&P 9/40 magazine with a built-in rail adapter mount for the MantisX training device. It replaces standard magazine base plates, or airsoft or replica firearm magazines that have a base plate that is shaped and functions the same as a "real" base plate. (Note: it has only been tested on M&P 9 magazines, but due to design should work on M&P 40 magazines as well.) Although the mount is similar to a Picatinny rail, it is specifically designed for the MantisX and its mounting bolt and so may not work for other devices/applications.
This replaces a standard base plate to allow for holster drawing drills, dry-fire practice with a laser/light on the primary rail, or other similar uses of the MantisX system where the normal M&P rail cannot be used; it does not increase magazine capacity or otherwise modify the functioning of the base plate beyond this.
(Please contact me if you have need of a similar type of magazine base plate for a make/model of firearm and/or airsoft or replica firearm that MantisX does not already make a rail adapter mount for, as I would possibly be interested in designing it as well.)