Dirty Brass Question...

[gene10pntr]

What causes some brass to be really dirty after shooting and some are pretty clean? Is it caused from the brass not expanding in the bore enough and getting blow back or the brand of powder? Too much crimp? Does the OAL have some thing to do with it too? I'm sure it's been asked before by many,just can't find it on here.

[Oklahoma Rebel]

I think low pressure is one of the main reasons, I know some powders burn dirtier than others, but the soot on the outside of the neck is definitely low pressure, and the brass not expanding to make a perfect seal.-Travis

[popper]

Dirty neck is usually blow back of soot. Could be oversized chamber neck or low pressure or both. Or burn rate of powder wrong. Not really a problem. Now soot all the way on the case (not dangerous) I'd sure want to find the reason. Ring of lead on the neck outside - find the problem.

[Grmps]

they are both right, I'll try to explain more simply

The case needs a certain amount of pressure (from the powder explosion and resistance of the boolit crimp and entering the rifling) to fire form to the chamber (expand the case to fill the chamber) thus preventing and blow-back

[Walter Laich]

straight walled cases are more prone to this than 44-40s or 30-30s

[GhostHawk]

For me the clear cause and effect happened in .45acp.

I had started with 5.5 grains of Red Dot and a 230 gr LRN cast boolit.

Shot fine but was a bit more "bark" than I liked.

Dropped to 4 grains of Red Dot, still shot ok but I had sooty cases. Real sooty, especially the half away from the base.

Went up to 4.5 grains and had clean cases again, and less bark. So that is where they stay.

Not enough pressure, so incomplete ignition, cases don't seal tight. Gas blows back carrying soot with it.

That's my story. YMMV

[brewer12345]

My lower pressure 38 loads usually end up with somewhat sooty cases despite the fact that I crimp solidly. Heavier loads in the 357 range usually leave very little mess.

[gene10pntr]

Thanks for info! Lower pressure makes more sense because the real sooty brass shows more if the gun doesn't cycle. I've been shooting some coated cast boolits and even the end of the gun (SR 9) has a lot of soot too,would low pressure cause this also? Never been this dirty before shooting plated boolits

[GhostHawk]

Easy way to find out.

A clean gun.
B load 5 rounds with + half a grain of powder (but below max)
C Load 5 with + 1 grain (still below max?)

Shoot em. Look at the brass, look at the gun.

There is also a difference in powders, some are harder to light off. Some are easy.
Some like a harder crimp to help raise pressures. The devil's in the details.

[Wayne Smith]

There are some powders that require a certain amount of pressure to fully burn - ball powders are prone to this. Not enough pressure, incomplete burn.

[Andy]

definitely seems like reduced loads are always the dirtiest for the reasons given above

[jonp]

All brass is not equal in hardness. Pressure that will cause one brand to seal will not fully expand another with the same load

[6bg6ga]

I concentrate on what gives me accuracy. To be blunt they make and sell ultrasonic cleaners and tumblers to clean your dirty brass. Chalk it up to part of shooting.