Dirty cases after firing

[Vleder]

Hi all
I have recently had some very dirty cases after firing, black powder all over the case and down to the rim, not all the cases and not all the same measure of dirt but nevertheless not what I expect should happen. Have spoken to a few gents and could be neck tension problem, lube on cases, dirty chamber, low pressure etc.
Herewith my details so if anyone has an opinion please feel free to guide me as well:

Redding match type s dies with nitrade/carbide bushing, .335 size.
Lapua cases, 308 win, Nosler Custom Comp 155g bullets, 42.2g S335 (local powder), COAL 2.860 (measured to touch the lands at 2.883). I am also using the match seating die from Redding.

Do not think it is low pressure with the given load, this did not happen with lower charges of 41.5 tot 42g and slightly shorter seating depths (2.850).

I want to try a smaller (.334) bushing and see if this improves the situation but I suspect as my other loads are not showing this problem that I might be the culprit with a dirty chamber and not properly cleaned (resizing lube) cases before firing.
Anyway, here's a pic of the offending case, this was the worst one, not all looked like this,
thanks for any advice guys.

 

[LRSickle]

My guess was low pressure loads but your not getting it at 41.5 so that doesn't make sense. I've seen low pressure loads do that and it looked exactly like your cases.
Lube would be my second guess.

 

[Joe King]

How many reloads do you have on these cases? could be their work hardened need to be annealed.

 

[Vleder]

Joe
Only about 1 or 2 reloads on these cases, and the loads have been mild, 41.5g, only recently tried getting a bit more speed and increased to 41.8, 42 and 42.2g, just these 42.2g which has given this powder residue, will test some more loads this weekend and ensure that the cases are clean and chamber clean as some suggested that some lube or dirty chamber can be the cause. Hopefully it is.
If not maybe neck tension, I have ordered a .334 bushing to see if that will improve the fit as I think my bullets are seated quite long (2.860) and possibly the shank pressing against the neck is less thus less seal thus less pressure (sorry my best layman explanation).

 

[112Savage]

My guess would be dirty chamber full of cleaning solution. If you leave any copper remover or something like ballistol it can cause discoloration like this. The brass that I have had this happen to have never been as dirty as yours though. They had a mottled blackening and graying of the brass. Good luck

 

[Joe King]

My guess would be dirty chamber full of cleaning solution. If you leave any copper remover or something like ballistol it can cause discoloration like this. The brass that I have had this happen to have never been as dirty as yours though. They had a mottled blackening and graying of the brass. Good luck

That's what I was thinking actually

 

[Lefty7mmstw]

What was the ambient air temp when the first(41.5) and second(42.2) series of rounds were fired? If it was significantly colder, you could have a borderline ignition problem. When it's hot powder lights easier and you can sometimes get fooled into thinking a standard primer is fine when you should be using a magnum. I've seen it more in varying accuracy, but sooty shoulders is somewhat common too. The lead is to switch either powder or primer and see if it stops.