1) Find out what your max COL for your rifle and that bullet
2) Reduce this by 0.020" to start with
3) Determine powder/charge range that gives the best accuracy
4) Vary the COL up to contact with the rifling/lede to about 0.030" short and see what COL your rifle likes with that particular bullet
To do this best, get a case length gage that measures from the ogive of the bullet and not the bullet nose.