Four years' worth, but if you can afford it before Oct '16 (and keep the same gun types), two or three times as much. Ammo prices began going up more than a month before November '08.
The only risk is that your home can burn down, in case the ammo is not insured or protected.
My extra stash for every gun is set aside for upcoming retirement, which covers any panic(s). The extra imported 9x18 Mak and really large heap of 7.62x39 is a 'hedge' against possible future high tariffs on all imported ammo (many politicians and US ammo companies would love this), or bans on any Russian ammo. Russian relations could get worse. Two nights ago I could not Identify any Ukrainian x39 via "Gunbot", and very little Romanian.
If an SKS or AK clone were used in a mass tragedy, some politician might designate the ammo as "high-powered military munitions", and most tv viewers would believe it.
A friend of my wife is known around town as a concert-level pianist (from Rochester NY), and considers me to be sort of "out there" despite my career,
due to hearing about all of my guns, and if she only knew how much ammo...