This is because the Afghan military has been equipped with Russian weapons from before the U.S. invaded in 2001. These have been replenished over time with similar small arms and artillery. This approach is being taken as the soldiers and security personnel are used to these weapons and it can be supported by existing stocks and facilities. Weapons and ammunition will be made in former Warsaw Pact and Eastern European countries like Bulgaria, Serbia and Romania.
ATK announced yesterday that they completed a task order from an earlier contract awarded in December, 2008. This was worth $87 million and was done ahead of schedule. ATK was responsible for managing the supply chain that procured and delivered the small arms ammunition, rockets, and grenades. These contracts illustrate some of the challenges of integrating a nation like Afghanistan and in some cases Iraq where suppliers not traditional to the U.S. or its NATO allies already exist.
These contracts were awarded after a first attempt failed spectacularly due to the fact that the company contracted with was run by a twenty-three year old who was getting ammo from Albania. This collapsed when an explosion occurred at a dump where the ordnance was being recovered and it was found that the equipment was Chinese made, was old and prone to failure.
Hiring a reputable, established company like ATK made much more sense for the U.S. Government, Afghanistan and the needs of their troops. It is not uncommon in the world of international arms trade especially for items like these that non-standard suppliers exist but for a situation like this a traditional company is more effective even if it costs more.