It is a completely made-up name;
Graz is Dirt in russian, and
Burya is Thunderstorm.
The closest matches i can think of are:
*
Gryazev-Shipunov GSh-18 pistol
http://world.guns.ru/handguns/hg111-e.htm
* Yarygin PYa a.k.a. "
Grach" (rook)
http://world.guns.ru/handguns/hg50-e.htm
or
* SPS /
Gyurza / Vector
http://world.guns.ru/handguns/hg25-e.htm