I use .50 cal Army surplus ammo cans. (Midway USA is just up the street from me, and these ammo cans in very good condition are usually available from them at very reasonable prices.)
I purchase pistol ammo from Target Sports USA a case at a time (to get the free S&H), usually purchasing a new case in a given caliber when my current supply in that caliber gets down to half a case. So, I use two .50 cal ammo cans for every caliber. Overflow goes in a .30 cal ammo can for each pistol caliber. My pistols shoot .357 Sig, .40 S&W, and 9mm Luger--so, six .50 cal and three .30 cal ammo cans for me.
I don't really "store" my ammo per se (in the sense of squirreling it away). This is simply how I "keep" it as I use it up.
rx7sig