The other day I watched Hornady podcast #218, about head spacing, etc. I highly recommend it. You can find it on YouTube.

One comment really caught my attention, because I've looked into it before. Jeff Siewert* said that lubrication on the case can double the force on the bolt face. This is mostly a "wear and tear" issue for the gun, but could be a safety issue too. I was taught long ago that the case had to be CLEAN: no dirt, no oil.

I see that the folks doing wet tumbling often use car wax, or similar products, to get cases shiny. I've been wondering how that affects the the way the brass case interacts with the chamber. In my mind it would have to reduce the friction between them. What do you think?

* Jeff Siewert is a ballistics engineer with 45+ years of experience. He's worked on everything from .177 air rifle pellets to 8" howitzers. He teaches classes on projectile design and ballistics to the US military and a slew of ammunition makers. Amazon just handed me his book "Ammunition, Demystified" about 30 minutes ago.

Here's another study on the same subject:
pubs.aip.org/aip/adv/a...t-of-seven

Good info, thanks