The YakB is a .50 caliber (12.7mm x 108, not the 12.7mm x 99 like our .50 BMG), 4 barrelled, gas operated(!), Gatling type gun used on the Mi-24 Hind D attack helicopter-troop transport. I found this while rumaging around in a scrap metal dump outside Kirkush Military Training Base (KMTB), in sight
This 'long gun' is used on the OH-58D Kiowa Warrior, aka the 'KW'. I spent over 8 years working on the armament, fire control, avionic (comm and nav), and electrical systems on this outstanding scout recon platform.
Photo from http://www.guncopter.com/oh-58d-kiowa/