Marco,
I usually use 5% citric acid (your Lemishine is basically that, but more expensive; I bought 10 lbs postpaid for about
$24 from Dudadiesle) and expose the brass to it until all oxide traces are gone. Heating to about 140°F in my Ultrasonic cleaner makes this very fast. I haven't monitored pH yet to see if I'm way overdoing the citric acid. I may be. I got that percentage from an old NRA article that said it had been the Frankford Arsenal brass cleaning solution at one time. Possibly in WWI. The decision to stop polishing for better corrosion resistance didn't come until the 1920's.
With extended corrosion time, at spots, the zinc in the brass will have oxidized preferentially, so that when the oxides are removed by the acid, you are left with a blemish in the form of a pink wash of surface copper. The surface copper wash, in turn, is so thin that it is easily tumbled off. I use the green Lyman corn-cob media to remove that stain, as it is faster than rouge, and is done in 20 or 30 minutes. It also produces a higher RMS surface finish, so it is not quite mirror shiny. You can follow-up with rouge to get a mirror polish if you like. After getting the pink out once, you will then be able to citric acid clean the case without the pink coming back.
My personal preference is for fairly bright yellow, but not mirror shiny. This is because my purpose is to make the brass as easy to spot in the grass as possible. At most matches the brass policing period is short, and tarnished brass ejected into the grass is effectively camouflaged. I also found out, when I tried nickel-plated brass for one match, thinking it would help me distinguish my brass from others, that a color-neutral mirror surface reflects grass-green, also camouflaging the brass in the grass. Mirror polishing brass-colored brass is not as bad, but it's not as good as a bright, dull yellow. If I could make brass a fluorescent color, I would.
Hounddawg,
You are missing some information on bullet cold welding. The first piece is that the gilding metal bullet jackets are drawn from is a form of low brass. It's about 5% zinc and 95% copper. The brass cartridge cases are made from basically just have a higher zinc percentage, giving them their yellow color, among other property differences. But they are both forms of brass and not completely dissimilar metals.
Second, cold bonding isn't caused only by galvanic processes. Even in a high vacuum, where oxygen and moisture are practically absent, two alloys containing one common constituent metal can exhibit some degree of cold bonding when pressed together for enough time. Physicists think it's because atoms of the common metal, at points of intimate contact between the surfaces, can, at the quantum level, become confused about which of the two kissing alloys they are actually part of. Once atoms are shared like that, separating the surfaces means pulling the trouble-making atoms out of one of the alloys, increasing the effort required.
Board member Hummer70, who was a test directory at Aberdeen Proving Grounds, said they had an instrument for measuring bullet pull and that he had measured as much as 600 lbs of pull on some 20-year-old 7.62 cartridges that had been properly stockpiled. These had about 60 lbs pull when they were new. That is still much less than normal start pressure, though, so it didn't affect their ability to fire. It would have increased peak pressure value a little. In QuickLOAD the pressure increase in a .308 Win from the extra 540 lbs of pull is around 1.5-2% depending on the bullet weight and charge level.
This phenomenon is well enough known that SAAMI actually has a spec for it called the Maximum Probable Lot Mean (MPSM). It is about 6% higher than the Maximum Average Pressure we usually see listed as the upper-pressure limit, but which SAAMI uses only for newly minted ammunition. The MPSM is a pressure limit for future samples from the lot during its whole lifetime.
Third, cold alloying between different metals can also occur if the required added energy is low enough, which is another way of saying the solubility of one metal in the other is high enough. Hatcher gives the example of tin-plated bullets used in National Match ammunition one year in the early 1920's. It was an attempt to cut down on copper fouling. Back then, bullet jackets were cupro-nickel alloy instead of a brass, and these tended to build up copper in lumps in a bore, so preventing that build-up was desirable for consistent performance both as to pressure and accuracy. They made and tested the plated bullets and all seemed well, so they manufactured the year's supply. When it arrived at Camp Perry and was issued for the matches, it was a few months older. Not only were pressure signs high, but some cases were ejected with the whole cartridge neck missing. The pit crews recovered bullets with case necks still attached and with rifling marks extruded into them. So this was actual cold soldering. Tin and copper make bronze, and apparently, some formed at the interface.
It's a world full of weirdness out there.
and the time factor. The case neck expands to release the bullet when fired. One more time; we had a member on this forum that fired the fifth round of a set he had loaded, he inspected the case' the case did not have a neck. He then went back and checked the first 4 he fired and found all of the necks missing. I never wondered if the necks were a little slow on the expanding sequence of events.