GI ammunition cans are the cat's meow. I have lots of the 50 caliber cans and have filled them up with pistol ammunition, in boxes, and rifle ammunition in boxes. However, loose stuff, don't fill a 50 caliber ammunition can with 45 ACP or 9mm unless you are a body builder. The cans must weight 70 lbs, they are heavy! I have one right now full of 230 FMJ bullets, that must be 100 pounds!.
The solution, was to pack the loose stuff in 30 caliber GI ammunition cans. Still heavy, but not neutron star density. Maybe 20 pounds at most.
GI ammunition cans can be tossed around, you can stack things on top, they are water proof, and if you shop around $5.00 to $7.50 is a good price for a 30 caliber can and $10.00 is a darn good price for a 50 caliber can. Walmart has Chinese 50 caliber ammunition cans in the Sporting Goods Department for $13.00 or so.
And, if you scratch your ammunition can, spray paint is your friend. I also spray the fronts and tops white and then write on the paint with a black magic marker to indicate what is inside. And when the contents change, a new coat of white paint changes the label!