Ol' Remus shares some ciphering:
Is 1,000 rounds for your battle rifle enough for a Mad Max collapse? Let's do some fifth grade arithmetic. Twenty rounds a week is 1,040 rounds a year. Or say a hundred rounds a month, which is 1,200 rounds a year. About the same. Figure three years and it comes to 3,120 to 3,600 rounds. Call it 3,000 rounds. So, 1,000 rounds seems low. If it's too much you end up with a surplus and bragging rights. If it's not enough you end up dead. Or you may end up dead with a surplus.
Look at it another way, a Mad Max collapse with extra Mad. One firefight a month using 160 rounds each, which is 8 twenty-round magazines, comes to 1,920 rounds per year. Let's be optimistic and assume you can survive thirty six gun battles—thirty five sure, but thirty six? Figuring three years it totals 5,760 rounds.
If the premises are reasonable, and who knows if they are, a stash of 3,000 to 6,000 rounds would be about right. More than you have? Cheer up, it's a near certainty something other than gunfire will get you anyway.