I have 12 of the M2A1 50cal cans and 12 of the M19A1 30cal cans. I recently picked up two of the 120mm smoke cans. I don't know the origin of where they were made, but can comment on them at least. My guess would be that they aren't made in the US, more like China or Pakistan or something.
The cans aren't quite as thick and heavy as standard mil cans. BUT they are more than enough for range use and storage. I throw in an aluminum oxygen absorber off of ama zon for about $10 each for the longer term storage. The seals work great - I tested with plumber smoke inside the can, which is basically putting a smoke bomb off inside the can. They seal quite well with no leaks. The seals look thick enough for long term storage, you can put vaseline or something on the seal if you really wanted to, but I didn't.
As I said, the metal is slightly thinner than what's found in the military, and the paint does come off a lot easier. Just having two beside each other in the trunk tends to scratch off some each trip. I personally don't care about this, as they are meant to haul ammo to the range and store them in my house for long term. I'll grab a can of spray paint if metal looks exposed and krylon them up.
The 30 cal can holds 1000 rounds of 9mm, and is about all the weight I want to carry on one arm. The 50 cal holds 1800 rounds of 9mm (with room at top) or 225 2 3/4" 12GA standard velocity or 250 2 5/8" 12ga Low recoil.
Now the 120mm smoke cans I received were CF or US surplus with the UN 0006 markings on them. Cans are great, and came with the two 120mm cardboard tubes. They are thick wall mil spec standard with some scratches and paint.. but the interior is flawless and the seals look brand new. The paint is neat and original from manufacturer, not spray paint from some grunt in his barracks.
shocking right 
