Russia’s Federal Protective Service (FSO) have announced that they will adopt the MP-443 “Yarygin” pistol chambered in the unusual 9x21mm Gyurza cartridge. This is the first time I have heard of a MP-443 chambered in 9x21mm. The 9x21mm Gyurza (not to be confused with the IWI / IMI / Israeli 9x21mm) has previously only been used with the Vector SR-1 pistol and SR-2 Veresk submachine gun.
Wikipedia has this to say about the 9x21mm …
The method of construction of the rounds allows them to be effective against both unarmored and armored targets. The bullet has a hard sub-caliber core contained within an outer sleeve and separated from it by a polyethylene layer. If the bullet strikes an unarmored target, it holds together to produce a wide wound channel. If the bullet strikes an armored target, the sleeve is stripped away and the core penetrates alone. The 7N29 AP loading fires a 6.7 g (103 gr) bullet at 410 m/s (1,300 ft/s) with 560 J (1,230 lb) of force, and will reportedly penetrate two 1.2 mm titanium plates, plus 30 layers of Kevlar, at 50 m (160 ft). The disadvantage of the rounds is that high impact velocities are needed for them to work effectively, so the bullets are relatively light to maximize their muzzle velocity. This means they will lose velocity relatively quickly, limiting their effective range.