RE: Clean barrel or Dirty
Oil in your bore will increase the pressure and shift the POI. It should be noted that increasing your pressure in your barrel can not only cause damage to the rifle but injury and thus a gun shouldn' t be fired with a oiled barrel! Best practice is to remove all oils prior to firing. In most cases rifles with a clean bore will not alter your POI, however this may not be the case with all rifles. Best way to tell is trial and error. I have 5 Cf' s that don' t alter POI with a clean bore and 2 that do only slightly, as such I clean mine as per usual before the hunt and final sight in session, but skip the oiled barrel part for long term storage.
I usually take 3 shot groups and let my rifles cool while I go down range to check my target. I would say anywhere from 3-5 shots depending on the loads and barrel, just make a note of what each gun does after you reach a certain heating point. However my best advice is make sure that guns is on cool, as most of us shoot the first shot with a cool barrel.