The latest version of the SR Submachine Gun from Russian design bureau TsNIITochMash is the SR 3 MP. The new MP model features a scope rail, two side accessory rail and, most notably, an optional underfolding stock instead of the side folder of the previous 3M model (or the over folder of the original SR3)
The reason for the under folding stock is to allow operators who wear helmets and/or night vision gear to be able to use the firearm’s optics without the stock getting in the way.
The SR-MP uses the genius 9x39mm round. The 9x39mm is a 7.62x39mm round with the neck enlarged to 9mm. It fires heavy, up to 260 grain, subsonic bullets.
[ Many thanks to Lionel for the photos and info. ]