Think yourselves lucky you can buy as much as you like... here in "Banned-it" country of the Uk, the amount of ammo for each calibre is limited to what they consider you need...
According to my FAC (FireArms Certificate), I can only possess 2000x .22rf, 750x .38/.357, 750x .223, 600x .308 and 500x 7.62x39.
When you buy ammo, it has to be entered on your FAC, and you can't buy more than your allowance.... but of course theres no check that you have used all that you previously had, so it is possible to stockpile more than your allowance... but obviously illegal...and the Police do have the right to do spot checks if they suspect you of anything illegal.
Edit... another thought is that over here, factory ammo is pretty expensive compared to the US, so most people who shoot a reasonable amount reload their own.... and that doesn't get recorded on your FAC...