The 9mm Luger AKA 9 x 19 has more case taper than many handgun cartridges. Setting up the dies optimally is critical for good performance of your reloads. I've run both the RCBS and Dillon 4 die sets. With the 9mm is especially important that the sizing die be adjusted so that the loaded bullet is visible and the case below it is a smaller diameter. Lacking this, the bullet on feeding will be pushed back into the case, setting up a high pressure event upon primer ignition. I set the taper crimp die to produce a .376" at the very tip of the case. This is a critical dimension. COL will vary with the bullet used. As expected, too short a COL will produce failures to feed. Too long won't run through a full magazine. Start the the recommended COL from your manual and adjust from there. I simply pull the barrel from the gun for this preliminary test, then try to a load a magazine full of them. If it works then its on to chrono and accuracy testing.