I would not use steel case in anything but Russian guns.. Mak's are ok as for rifles other than AK's and sks's, I dont like it in AR's but alot of others can use it.
As for Spam cans... I have stacks and stacks of ammo in those. What do you want to know? I try to get ammo my ammo in spam cans they store forever you know your ammo count and they pretty look cool. I have some of those cans for SHTF useage as well.
I'm with fatcat. I've shot thousands of rounds of steel case thru AK based weapons without any problems, but won't shoot it thru my other guns. It's been years but I do remember it as being pretty dirty, may have changed since then.
I do like battle packs or cans for storage, keeps it all together and protected.
It depends on what your shooting it through? A Glock will chew up anything you put threw it ! Same goes for the AK and SKS. I would not try feeding it through an AR. Also, they are quite dirty, but I have never had them foul my AK's, course you could shoot rounds from a clip full of mud and not jam an AK !