These are usually gun show pickups for me and the biggest problem i’ve had with them is not buying consistent sizes. Anyone that reloads ammo keeps things like these around because it’s a safe, economic way to store bulk ammo. Most of these are military surplus but some are not. These are excellent for keep your powder dry and keeping brass clean. I’ve also used them for gun cleaning supplies and store certain types of books. Back in the day I use to see bulk ammo buys that included ammo cans but not so much anymore.
If you aren’t sure what size you should get, go with the bigger sizes because you can always create levels and separate different items internally. Remember to label your stuff because they are marked for 5.56, 762 or 50 caliber. If you buy multiples of the same sizes they are easy to stack. These also make great gives for 10 year olds and do a nice job of keeping army men in the same box. *joking*
You can always get the lighter plastic ammo cans but they tend to not hold up to as much abuse if you are going to be throwing them around a lot, but their starting weight of being made of plastic vs metal does make them lighter. The metal ammo cans are from $22.99 to $36.99