Bullet Comparator Question

[StoneHendge]

Make a dummy and seat it at your desired depth according to your calculations. Just size a case (or use a virgin piece) and seat a bullet (no primer or powder). Put it in a mag, slam the bolt home, pull the trigger and see if it breaks, then see if you can extract it. If you can, measure the COAL and see if it shrank and inspect the bullet to see if it engaged the lands. This will tell you if it is indeed your barrel or if it's however your measuring. This is the only real way to confirm depth - I use the Hornady comparator but I find it to be prone to measurement error.