The US Army Marksmanship Unit has produced some useful YouTube videos for the average shooter. In the video below, Sgt. Joe Hein, an International Rifle competitor, discusses how to prepare for the first shot from a cold bore. That is, the first shot of the day which for many hunters may be the only shot of the day.
Sgt. Hein illustrates the difference in grouping for a cold rifle with a clean bore versus one with a somewhat dirty bore. You tend to get more consistent groups from a cold rifle with a dirty bore.
It's a short video but I learned something.