I wasn't sure where to post this question. I've been using an RCBS Precision Mic for my 110fp, 308 to determine bullet seating depths. The rifle is around 10 years old now. I have always loaded for it and have kept the load velocities below max listed levels. I use mostly the usual powders from IMR and lately Varget. Bullet weights range from 155 - 175 grains. I double checked the chamber tonight and found that the distance needed to touch the lands on the mic has increased by 0.015" over the years. Is this normal? I checked and re-checked the mic reading several times and it's always w/in 0.001" of my initial measurement. I shoot intermittently throughout the years and maybe sent no more than 2000 shots down range. Any thoughts?