This never occurred to me when buying ammo, but how do I open a spam can properly?

I turned the can upside down (with the lid against the ground), then went parallel to the side of the can with a screwdriver and mallet, with the tip of the screwdriver at a 45-degree angle. This helped create enough separation once I went around the tin to be able to pry the lid off. As the tip of the screwdriver is only going to be driven into the space between the lid and the side of the can, you won't have to worry about it hitting the primers. Instead of going all the way around, I've just pried it to where the metal bent back and ripped a hole open with a pair of pliers before.