Terrorists did not get to that stash, it was really heavily guarded. Now when u see an sks with no bayo on terrorist shoulder it means it's civil version for hunters and shooters. When it has bayo it's military version and I have no idea where did they get it as Russia supplies terrorists with very modern weapon. Probably from some paramilitary state guard services.
P.S. I am blessed as I saw thousands of crates of surplus guns in Balakleya, where they were delivered from salt mines to be serviced and the either sold overseas or deactivated for souvenirs. I can describr the feeling, it's really overwhelming.