I have a fairly substantial gun cleaning combo ammo storage/stacking table I built out of 4x4 legs, 2x6 framing and 2x4 supports under a 3/4 inch plywood top. I figured, I'll stack my ammo here along the back, clean guns here in the front, no big deal. over the last 18 months, I have stashed probably 8-10k rds of mixed ammo all in surplus ammo cans (223, 308, 9mm, 40, 45, 9mm, 22) last fall I noticed the table sagging. I had to put additional 4x4 against the back support. yeah, that didn't help. I had to take most of the ammo off and put it on the concrete floor underneath the table. Chit. and I have another 2k rds of various showing up this month.

My wife asked the same question as the OP.