I'm no rifle or reloading expert and i learn something new every day but this is my opinion and experience with seating depth. Every rifle is different and while some may shoot great with the bullet next to the lands some don't. I think seating a bullet at .030 is safe and really as close as you should seat for a sporting rifle. I have found that in most cases juggling components will get you the accuracy you desire and then if you want to experiment you can tweek it a little more by adjusting seating depth to see if it makes much difference in accuracy. I usually start at .030 off the lands and work on a load juggling components and if i find something that shoots really good and in most cases i do then i don't touch the seating depth at all. If i find a load that won't group very well with anything i've tried then and only then do i play around with the seating depth. When i do adjust seating depth i go out with the bullet .005 at a time until i'm next to the lands just to see if it makes a difference. I don't think seating depth plays as big a role in accuracy or is as important as most people make it out to be because i've seen rifles shoot tight groups with the bullet seated .010 off the lands and the same rifle shoot the same load just as tight seated .040 off the lands. There are several ways to find the OAL for a rifle. If you feel you must seat next to the lands you can make a dummy round and drill the primer hole out with a #7 drill and tap it with a 1/4-20 tap. Get a piece of 1/4-20 threaded rod about 4" long and slot the end so you can use a flathead screwdriver on it. Next seat the bullet so that it's short and off the lands. Next color the bullet with something like a marker and keep chambering it and taking it out of the gun and moving the bullet out using the threaded rod until it touches the lands and then back it off. You'll see the lands marks on the bullet when it touches or if you go to far the bolt won't close so just seat the bullet deeper away from the lands.
Another way i've done it is to use a dummy round and seat the bullet long and try to chamber it and if the bolt won't close then keep seating it deeper until it will. I use to use those methods and they always worked pretty well and got me close. I finally broke down a couple of years ago and bought a Stoney Point OAL gage with the bullet comparator attachment and it is simple to use and works great and i would recommend it to anyone. Good luck!