I mostly buy what I shoot. I have a handful of .30-06 rifles, so I keep a few hundred rounds for them. Lately it's just been the Korean stuff. I'm down to one can, so I should probably buy another can, if I see a good deal\
My OH NO rifle is an AR-15. My OH NO, don't touch it ammo is 2 cans of Radway Green on strippers and in bandoliers. I figure thats about 1.9 cans more than I wouold ever need, but there is no such thing as too much, is there?
After that I try to keep a case of 5.56 around for random plinking and practice purposes.
I have a few hundred rounds of .357/.38 I really don't shoot it that much.
I have about 2k of .45 ACP for the 625. I got a deal, but I'm not shooting that gun as much as I though I would. Maybe 400 rounds/ year.
I really shoot alot of 9mm. I shoot 800 - 900 rounds a month. I know it sounds like a lot, but it's still alot cheaper than drinking. I'll wear out that plate machine yet!
.22 is so cheap, and gets used up so fast that I start getting ansty if I have less than 5000 on hand. One trip to the range with a bunch of friends, and it's easy to burn through 5 or 6 bricks, ya know? On top of the cheap plinking stuff, I have a brick of this and a brick of that of all kinds of premium target ammo for the Anschutz. Maybe 8 or 9 bricks total.
I keep a flat of 12 gage and 20 gage birdshot on hand, in case I get invited to a midnight skeet session, and can't pick up a few boxes at Walmart on the way. It happens!
Maybe 200 rounds of .303.
I guess that pushes me a little over 10k. Don't make me pull out my calculator!