Properly stored ammunition can last a lifetime but Russia has a bad track record of improper storage that leads to massive explosions and death.
www.vice.com
Take this as you will but considering Russia has been reported as buying ammo from North Korea of all places, the idea of them burning through their ammo stocks to the point they're willing to pull the deep storage stuff seems at least somewhat plausible.
And I don't think we need to go over the fact Russia kinda sucks at the maintenance part of the equation on a lot of their stuff. So look forward to more Russian ammo depots spontaneously combusting in the new year, I guess.