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I have often wondered if excessively polished brass performs differently in the chamber to military brass. Is it akin to putting a cartridge into an oiled chamber? I like to see my brass clean on the outside and once I left some brass in the tumbler for three days by mistake - it came out polished and almost without a blemish, whereas military and commercial brass can be quite rough by comparison. Is there a need for the case to grip the chamber that can be compromised by overly polished brass?

Think of it the other way around. If you used the same ammunition in a rifle with a smooth, hand lapped chamber versus a rifle with a very rough chamber would you expect to see any difference? I don't think it would make any really difference

The only improvements that shiny cases offer is to not damage your dies during resizing (dirty cases may have trapped debris which could potentially scratch your sizing die) and to aid the reloader in identifying damaged brass.

I just wonder if it is not the same as putting an oily cartridge in the chamber. If there is a problem then hand lapped chambers and polished brass might reach a point where the cartridge does not grip the chamber on firing. Not something I have ever experienced but theoretically it could pose a problem, particularly with lighter charges.

The only reason for cleaning cases is to make it easier to spot defects other than that it serves no purpose. Brass is a lot softer than hardened dies a dirty case is not going to make any issues with a reloading die. Try machining a Lee or any other make and you will soon discover how hard they are. Then try machining a brass case easy as.

In "Handloading for Competition" written by Gel Zediker he explains that highly polished brass can cause the brass to not grip as well in the chamber placing an increased rearward loading on the bolt, lugs and action when compared with the same load fired in clean, but not polished brass.

I wonder if Glen said how he measured that increased rearward pressure.

Unfortunately I need to use wet tumbling for my black powder brass and they come out all horrible and shiny, however if I leave them in the liquid for few hours after tumbling the take on a nice dull look. Easy on the eye and clean to boot.

As has been said cleaning is so I can see any faults in the case, also I don't want dirt and grit in the dies it certainly won't hurt the dies but grit in the die will scratch the cases which is something I don't want.