Stop! Bolt time!
I'm finally done with the dual-platform!
It's an SMG as requested and a 6-shot bolt gun for stealthy kills! Caliber? 5.45mm.
It also has... Wait for it! Direct satellite uplink!
That piece of tech is actually called the Umbrakinetic Industries Weapon and Armor Integrated Comunication and Scanning Satelite Battle Computer.
EDIT: The bolts fired from the revolving mag are not propelled via gunpowder. A coil is used. Kinda like a rail gun.
I hope that satisfies your need for everything to be realistic!