SC\’s list of possible culprits causing the length variation is spot on, but does not address bullet to bullet dimension variations. I\’m not sure if the Lee bullet seater uses the bullet nose or the ogive as the surface is contacts when seating. If it seats using the bullet nose and the bullets vary in length (which can happen) the COAL will also vary. The ogive wrt base location is more consistent, I\’m guessing, due to the way the bullet are formed.

If you\’re measuring COAL I suggest you invest in a Hornady Lock-N-Load Basic Bullet Comparator set (or its equivalent). They go on sale periodically at places like Midway USA.

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