Case Length and Case Trimming

Q. How does case length and Case Trimming affect reloading accuracy and chamber pressure?

A. The case’s neck should be trimmed to length for the first loading and for each loading thereafter. Factory cases are not trimmed, therefor are not square, nor are they of consistent length. Each time a case is fired, the brass flows in the neck area, getting longer with each firing. With extremely soft brass, one shot may stretch the neck all the way to the barrel throat. Normally brass may be fired several times before trimming is absolutely necessary. If the case neck is allowed to get long enough to touch the barrel throat, closing the bolt will drive it forward, wedging the case between the throat and the bullet. It may even crimp the case into the bullet. When the cartridge is fired, the pressure has to build high enough to free the crimped bullet out of the case. Loss of accuracy is a given at the point. A more important question in this situation is raised with the safety of the round in the chamber. We want the bullet to leave the rifling and find a tight group; we certainly don’t want to build pressure to the point that the bolt will be leaving the rifle!!

Posted in: Case Trimmers & Accessories FAQs