The easiest method I have found,is to make a long dummy round,no primer or powder,just in case the bullet jams in the rifling,no powder to clean up if it does.You will need to do this with each different style of bullet you intend to use.
Soot the bullet with a candle,and chamber the round,the bullet should be pushed back into the case,with about .020"-.050" of the shank into the lands.Repeat this,by seating the bullet in your dies,until a sooted bullet comes out with no rifling marks.Measure OAL at this point,make a note of it,and then with another fresh bullet/case,wind out your seating stem one full turn,seat the new bullet/case at this measurement (RCBS/Redding) this will be equivalent to .036".This should be in the vacinity of .030" off the lands.Do not soot this bullet yet,chamber,make sure there are no rifling marks,and continue.Seat deeper,by 1/8 turn at a time while chambering each time,as soon as you touch the rifling again,back out 1/8 turn and measure,make a note,this should be about .005"-.006" off the lands.By comparing the two you can get your OAL just right.
Soot that bullet,and see if there are rifling marks ALL around the shank,if they are only on one side that means the ejector is tipping the bullet to one side.By adjusting your seating stem with small turns,1/8 is fine,you should be able to get the bullets just touching,say .005",or just missing.
KEEP this dummy round as a reference,and you can adjust the seating stem to whatever distance you want into the lands or out of the lands.
If this fails,you'll have to get an ogive comparator from Sinclair etc.