Just wanted to run this past you guys. This is the first time I am messureing the chamber length, and then using this info to let me know when it is time to trim my cases, and I didn't want to blow up my rifle, or kill my self. Unless this method is way off course, and if so plese point me in the right direction. 1. Chamber length for my factory Rem 300 Mag is 2.6515. I got this buy using the sinclar chamber length case plug. Messured from the bottom of the case to the end of the plug after chambering the case/plug. 2. My average length case that has been fired once is 2.615. 3. My book tells me to have a trim length of 2.610. Now I know this length will allow my to chamber this into any rifle with out having the end of case sit on the rifling. So here is the question. After each time I reload my brass I need to make sure that the length of the case does not exceed 2.6515, and if it does I need to trim it back a little. ****DO I HAVE THIS RIGTH, OR AM I GOING TO KILL MY SELF****? 4. If I have this senario right, how much should I trim off of the case once the case length is greater than 2.6515? Thanks for helping out a new guy.