These are great - MTM Durable Ammo Can w/Double Padlock Tabs

You can put a ton of ammo in these and they stack perfectly on top one another. The double latch on these newer models is also a plus. They are not caliber specific so you can store multiple calibers in the same box if you are going to the range with several different firearms as I often do. I also use them to store half dozen fishing reels on a long trip to keep them from getting banged around in a pickup truck or airplane.