I use the Hornady (previously Stoney Point) modified case and the bullet I'm going to load for. It will allow you to get a total length of the cartridge in question with the bullet you are using to where the rifling begins. Once you know that length you can begin experimenting with different COAL's to find the spot where your rifle likes that bullet placed. You can check youtube videos for demonstrations of use. I hope this all makes sense.
Same here. There are other ways, but the system above is the easiest I've found. If you don't want to invest the money right now, try this. Take a fired case (not resized) and press the mouth of the case on the bench slightly denting it. Now take the bullet you are wanting to load, color it completely with a black magic marker and insert it slightly into the dented case. It should insert with a little resistance caused by the dent in the case. Just get it slightly started into the case. Chamber the case with the bullet inserted slowly and close the bolt. Open the bolt and extract the case. The bullet will either be seated to contact length or will be stuck in the chamber. If so, carefully knock it out with a cleaning rod (or a bounce or two on the floor). The marker will be scraped off the bullet by the dent in the case mouth. Re-insert in the case to the scrape line and measure the overall cartridge length with your caliper. You now have the maximum length at which the bullet will touch the lands and can adjust accordingly. Hope this helps.
If you can, buy the Hornady system. It is not very expensive (about $30.00) The only drawback is that you need a modified case (about $5.00) for each cartridge you load.