Hi, Eddie,
Welcome aboard, matey!
As you can see, there has been an excellent response to your problem and hopefully, by now, you've solved it. When you trim each end of your tube/blank are you using the appropriate sized barrel trimmer? Ideally, you should increase the diameter size of the staffs on these trimmers with each increase in the diameter of the brass tubes, so that they are a snug fit. Failure to do this often results in an off-centre trim.
Bob.