Cartridge Brass and alloy composition

[Grouchy Bear]

[J-cat]

You can’t cast brass cases. They have to be drawn in order to have the correct hardness in the case head so they don’t burst under pressure.

[JackEllis]

Might want to watch this video about making .22lr. It's indicative of the steps that are required to make brass rifle and pistol cases.

Then start at 1:37 in this video to get an idea about how the case would be formed. The video describes the how and why of aluminum cans but the process for cases would be similar.

In addition to the fact that rifle and pistol cases have to be drawn, I would imagine you'd have trouble casting a thin walled cylinder to the proper tolerances, which is another reason they're drawn instead of being made in a cast.

Here's another video that shows how rifle cases are made.

Regarding the specific alloy(s), I'm guessing the 70/30 formula is a bit squishy, but that's based solely on a visual examination of a few tens of thousands of rifle and pistol cases. Newer PMC .223 cases seem to have a bit of a reddish tint so they may have more copper than some of the others.

[J-cat]

I wouldn’t guess the composition from appearance. You can control the color with chemicals used during final cleaning/polishing. The same case can come out white to golden to dark purple depending on the amount of acid in the mix.

[justMike]

A little Gargling found this. Pretty detailed too!

http://bulletin.accurateshooter.com/2011/09/cartridge-brass-alloys-revealed-by-x-ray-spectrometers/

[divingin]

Quick overview of making rifle brass:

https://www.petersoncartridge.com/technical-information/drawing-brass/

Video on making handgun brass:

https://www.starlinebrass.com/videos?id=2377

[74c5]

That is the right ratio. C26000 has always been one of the callouts for cartridge, or yellow, brass that's easiest to lookup. Plus or minus 1.5% on the copper content is allowed per the ASTM B36 spec. There are other callouts via newer, older or more preferential specifications. Getting the right heat treat, cold work and annealed where it needs to be to make a cartridge is the real trick.