This next technique requires the use of a borescope. I hate a carbon ring, and one of the best ways not to have one is to have a short distance between the case mouth and the beginning of the leade. We all need to trim our brass, but we don’t need any more room between the case mouth and the beginning of the leade than “just enough.” In other words, in a 6mmBr maximum length is 1.560 and recommended trim length is 1.550. I take an old case and drill out the primer pocket just enough for my borescope to be placed through it. Then I place the case into the chamber and put my borescope through the enlarged primer pocket and push it up to the point I can see how the case mouth relates to the beginning of the leade. If 1.560 gives me plenty of room, there is no need for me to trim it back and make a larger area for the carbon ring to grow. Also, this technique supports the borescope and centers it in the center of the barrel, so you can use this when scoping your bore.