The GSh-18 Pistol can fire a very hot (similar to 9mm +P+) 9mm Luger round loaded with an AP bullet called the 9mm PBP. It has the capability to punch holes through 8mm of steel or a Class III bulletproof vest at 20 meters. This video (from RIAN) shows off its capabilities:
Defense Review wrote about the pistol recently.
H/T: Reddit