Are you trimming the cases? Long cases run through a die set up for proper length cases will give that result. If you are using a flat based bullet, be sure you are chamfering the mouths enough for the bullet to enter the case with out too much resistance. The flat base could be hanging up on the case mouth.
In life, strive to take the high road....It offers a better field of fire.
"Robo is right" Fuzzball