Heat, a BIC lighter will do it, but I use a propane torch on low heat. Wear welding gloves, heat it up a little and pull it apart, it doesn't take very much and the hull and the plastic in t e base will split from the brass. The brass is only plated, so be careful don't scratch it or you will have some sort of cheap steel look. That was one of the reasons I went to glue ups with the Osage or yellow heart for the brass look.
You have to JB weld them in place, or you can drill a hole though the primer and use a brad. The primers are tough to drill, again steel, they are not made of copper.
Marvin