RE: im a beginer and have a question about seating my bullets
I have done this in the past:
Seat a bullet into your case far enough out so that it is guaranteed to touch the rifling. Use the bolt to force it in. Extract this case and measure it with a caliper. It is not, in my opinion, a good idea to use a loaded cartridge to do this; use an empty, unprimed case to do this.
Start backing the bullet a bit away from the rifling by seating your bullet deeper in 0.010" increments. You should make several rounds up at different seating depths and see which depth gives the best accuracy. Often, but not always, the closer the bullet is to the rifling, the better the accuracy. I found that about .010" to .020" from the rifling is best in my .30-06.
If you make ammunition where the bullet touches the rifling, be EXTREMELY careful to back your pawder charge away from the maximum in your loading manual. The pressure buildup in a maximum charge with the bullet touching the rilfing can be very dangerous. Look out for signs of excessive pressured, described in your loading manual. If you see cratering around your primer, if the bolt is "sticky" after firing, if extraction is difficult, you are in a dangerous pressure regime. Cease firing that ammo immediately, and use a bullet puller to remove the bullet & powder so you can start over.
Good luck, and have fun!