The primer tray is pretty much like the rest of the machine; fantastic when it works and a complicated butt pain when it doesn't. There's a few of things that have to be timed correctly for it to work right. Two pieces of advice I can give you are to carefully check the machine for proper timing BEFORE you start loading, and use the LEE CARBIDE factory crimp die. It's cheap and helps you turn out factory quality ammo.
To get back to the timing thing, once you get it all set up you'll get a "feel" for the machine. There should be no forcing anything, nothing should be stiff or hard to operate. When you're loading ammo if that "feel" changes, even slightly, find out why and fix it. Could need lube, could be a live or spent primer caught somewhere, could be a few grains of spilled powder making things drag. Whatever it is, find it and fix it immediately. Also, never force the machine to do anything or you'll be bending or breaking parts that RCBS may not sell anymore. Lightly lube the parts that rub when you operate the lever. Because of the way compound linkages amplify drag you'll be amazed that what felt like a jammed machine was just dry from lack of lube.