Hm what have you got the Clip Size (under "Reload") set to? Are you seeing any warning/error messages? Are you using a custom animation for the firing? If you "Log Events" on the AnimatorMonitor component, do you see the "OnAnimatorItemUse" event being called as expected?
These are all kind of shots in the dark really as I can't see anything wrong with your setup. What version of UCC are you on? If you can't figure it out, you could DM me a repro project and I can take a closer look at your case.