I have opened these cans with both an old chisel and the can opener you get with a case of ammo. To be quite honest, I had better luck with the chisel-it took much less time. You just need to be careful and keep the chisel as close as possible to the edge without hitting any cartridges.
I always get amused thinking of some poor Ruskies out of ammo and looking for a way to open this can or even worse the 7.62X39 can with the enemy 50 yards away and advancing on the run.
The grinder worked well and the "39" can is a real gut buster when you get old, like I am.
Why use a 50 pound bomb when a 500 pound bomb will do?