I like to use a permanent marker for testing overall cartridge length in rifles. I mark the ogive of the bullet and then carefully chamber the round and remove - if there's contact with the lands of the rifling, it will show on the bullet.
This is a crude way of checking this, but it does keep you from jamming the bullet into the rifling.
I have a Stoney Point Overall Cartridge Length Comparitor tool with various caliber modified casings to get a more exact read on this.
I will often start with the bullets loaded to .005" off of the lands - test propellant charges and then, I'll take the best one and then vary the bullet seating depth to see if I can improve on the the accuracy.
Sometimes, the best accuracy is with the bullet seated way off of the rifling, though usually, not. Usually it's best nearer to the lands.
Also, interestingly, I have found two 'sweet' spots with a load - one near the lands and the other with the bullet seated farther out...
What this is really doing is fine-tuning the exit of the bullet from the muzzle in relation to the barrel vibration patern.
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