If you already know this, just ignore me. Lake City military brass has the primers "swedged" in place because they are used in full automatic weapons as well as semi-auto. Before you can re-prime this brass, the "swedge" must be removed. There are a couple of ways to do it but it must be done before you can install a new primer. You only have to do this step the first time you reload the brass. It is excellent brass but that first reload requires an extra step.
Enjoy the new hobby
edit: Guess I should have explained the possible methods to remove. You can use a case deburring tool to "cut" the extra piece out of the primer pocket but it is tedious and you have to be careful not to enlarge the pocket. The other alternative is a tool that RCBS makes which actually "pushes" the swage back into the edge of the pocket and sizes it for a new commercial primer. Perhaps one of your friends already has this tool. I was lucky as a long time reloader friend of mine has one and taught me how to use. it.