Plunk Test:
Make up a dummy round.
Remove the barrel from your gun.
Drop a dummy round into the chamber. The sound this produces is usually a "plunk", hence Plunk Test.
If the bullet is seated long, it will headspace on the rifling and not chamber completely. (Compare the rim to the barrel hood). You want to seat the bullet deep enough to fully chamber without touching the rifling.
If you seat the bullet in the case without crimping, you should be able to seat it long and push to into the chamber with your thumb until the case headspaces properly on the case mouth. The bullet will then be touching the rifling. Set it a 1 or 2 hundreths deeper and you have the proper COL for that bullet in your barrel.
Some barrels may have a long throat and the resulting COL is too long to cycle from the magazine, so you will need to check that as well. If it is too long, just seat it deeper untll it cycles properly.
The COL in the manual is the COL for that load data. It may very well be too deep and represent the minimum COL, rather than the recommended one.