From what I have heard and what I know from working with lubricants, I would consider this a dangerous practice. The case uses friction against the chamber wall to reduce load on bolt face. Using lube in this location will reduce this friction and increase the possibility that a tapered case can slide out of the tapered chamber, adding to the already considerable force on the bolt face. For me it is always a dry oil free chamber and dry oil free bullet.
Visualize the case as a slippery water melon pip between your fingers.
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