Why are some brass casings shiny on the inside?

[Dewey 68]

I've noticed that after I wet tumble brass, some makes are shiny on the inside of the case, and others are dark. I like the shiny stuff because it's easier to see the powder in long skinny cases like .38 special and 357 magnum.

Does anyone know why this is? I'm wondering if it's the way the case is formed, or is the stuff that's only shiny on the outside plated with a different alloy? I would think that they would all get polished on the interior the same during the tumbling process.

 

[mdi]

I can honestly say in 40+ years of reloading I have never considered the interior appearance of any cases I use to be of any importance. As long as there is no "coating" of dirt/gunk, etc. it's good to go. Until wet tumbling became popular I can't remember anyone being concerned with pristine, glossy primer pockets and case interiors.

But to answer your question, cartridge case alloy can vary a bit from manufacturer to manufacturer and can react to different chemicals differently. Your tumbling methods and materials will cause more variations than case alloy.

I have looked in every case I charged with powder since 1971 (I had a squib in 1970) and the shine on the interior made no difference at all...

 

[buba68]

Never really pondered about the inside of the case being shiny after cleaning but I have wondered looking at a lot of cases before cleaning that some have insides that look like they have never had a powder charge fired in them. Not sure if some powders are just cleaner than others or if some high pressure loads burn cleaner and keep the inside of the case cleaner after firing.

 

[tightgroup tiger]

I see the same thing as MDI in my Ultrasonic cleaner and I think the once fired brass is still clean, and shiny smooth because it hasn't be blasted enough with powder yet to roughen the finish.
With the brass that I shoot a lot, well, it all started out shiny on the inside when it was new or only fired a couple times but the more it's fired the darker it gets.
I don't have any that is black inside but most of my brass doesn't reflect light very well any more. It's clean and copper colored, just the inside isn't shiny smooth any more.

I actually look for the clean, shiny ones and consider them truly once fired.

 

[9mmepiphany]

...after I wet tumble brass, some makes are shiny on the inside of the case, and others are dark.

Does anyone know why this is?

One of the major reasons to go with wet tumbling is to clean the inside of cases and primer pockets. If you aren't getting clean insides, it isn't likely due to the manufacture of the case as much as it sounds like a wet tumbling process issue

Are you depriming before tumbling?
Are you using stainless steel pins?
Are you using Lemi-shine?
Which detergent are you using?
How long are you tumbling?