hey, gtbehary...
I actually heard of someone ordering the same stuff from Cheaper Than Dirt a short while ago and experienced the same deal... different marking on the case.
This guy happened to go ahead and open the crate up, and take a look at what exactly there was in there. Lo an behold, it was 7.62X54R. You may want to contact the peeps you bought it from to be sure, maybe they can shed some light on it for you, without breaking a seal on a tin...
Best luck to ya