Weird soot pattern on spent case

[Hoons]

On all the spent cases I'm seeing about half of the outside covered in soot. Is this because the chamber is too big and brass cant expand enough to seal it? This is on a new gun.

[DaveInOroValley]

Reloads or?

[Hoons]

Yes...

[DaveInOroValley]

I would first suspect the powder. If it is a new batch shouldn’t be a problem but I’ve seen older powder do odd things. If the powder smells off that would be a clue.

[Duck Killer]

Some pistols leave that mark. I believe it is HK.

[19K]

Not high enough pressure to completely seal the round.

What is your load data?

[Kurgan]

I agree. Looks like an H&K fluted chamber.

[Hoons]

Some pistols leave that mark. I believe it is HK.

It is on an hk. So it is normal? Any idea what causes it?

[Hoons]

Not high enough pressure to completely seal the round.

What is your load data?

200gr LRN with 5.6gr bullseye

Looks like the culprit is fluted chamber of hks...

Thanks calguns!

[Kurgan]

Some H&K pistols have a fluted chamber as part of the operating system. It allows spent gasses to be released and aids in extraction.

[Hoons]

It seems odd that only about half of outside case exhibit that.

[74c5]

MP5 I was issued would do that. Not all the time though. It is a timing thing where the rolling block delay would have a different timing (unknown if longer or shorter) and pattern the brass.

[Itsrockysmodernlife]

On all the spent cases I'm seeing about half of the outside covered in soot. Is this because the chamber is too big and brass cant expand enough to seal it? This is on a new gun.

Hk mp5s and some of their pistols do this.

[ClayBreaker]

Not high enough pressure to completely seal the round.

What is your load data?

I suspect low pressure as well. My old 45 colt reloads did the same, but not my 9mm's or 308's

[pacrat]

It seems odd that only about half of outside case exhibit that.

Blame gravity.

Portion of the case already in contact with bottom of chamber, will show less soot. Since the bottom of the case is already in contact with chamber.
The case, at moment of ignition, expands IN ALL DIRECTIONS EQUALLY.