Soot/Carbon on Outside of Cases?

[ScottRiqui]

The ammo used was factory, not reloads (I'm still working on gathering up a sufficient quantity of .380 brass before I start reloading it), but I figure you guys probably spend more time examining your spent brass than those who don't reload, so I thought I'd ask here.

Most of my spent cases fired from my .380 have some carbon deposits on the outside of the case. Here's a picture of one of them (sorry for the cellphone pic, but I think it's clear enough.)

It appears that some of the hot gases from the burning powder are leaking back between the case and the chamber wall. I've seen this on other people's pistol brass as well from time to time, so I don't know if it's indicative of a problem, or just something that some guns do.

The gun used was a Beretta 84BB (about 25 years old, but very lightly used). The chamber and barrel look pristine - smooth with no visible pitting or deposits. The ammo was Winchester White Box, 95 gn FMJ.

Any insights would be greatly appreciated.

 

[JR_Roosa]

My .45s do that, even in my nice tight national match chamber. It's from exactly what you said...burning powder leaking back from incomplete obturation. Basically the pressure is too low to completely seal the brass to the chamber for whatever reason. Maybe the case is a little thick, the chamber is a little generous, the brass a little stiff, or whatever. Doesn't seem to hurt anything.

In rifle brass I see it as a low pressure sign and try to keep my loads above the level where I get bad soot so long as I'm not near max loads. My powder puff .30-30 loads do it with light bullets and light loads.

You don't want to push the pressure in the .380 since in a blowback action, you want the brass to be able to start moving back and ejecting while the bullet is still in the barrel.

It polishes right off in the tumbler.

-J.

 

[mikld]

Is your Beretta a straight blow-back action? If so it's possible the case is getting soot from gasses as it's being pulled out of the chamber.

Oops, didn't see the blow back answer in the above post...

 

[bossman]

Should clean up just fine after a run in the tumbler.

 

[Walkalong]

Perfectly normal. My blowback action AR 9mm leaves cases dirty to absolutely filthy with loads that leave cases clean to fairly clean in locked breech pistols.

That case looks a little too good to have come from a blowback design. It looks to me like it was fired in a locked breech design, and since I think the 84 is a blow back design, you are looking good.

 

[dacaur]

I get the same thing with all loads in my sub-2000, which is a blowback 9mm....

 

[m&p45acp10+1]

If it shot well the look of that case would not bother me. My .45 ACP LSWC loads give me sooty looking cases. They shoot great so I do not care.

 

[ScottRiqui]

Thanks for all the replies - I was a little worried that since the soot/blow-by is only happening around part of the case, there might be some flame-cutting going on in the chamber.

But since the chamber still looks pristine, I'm not going to worry about it. Also, I sorted through fifteen gallons of brass at the range today, and I saw a *lot* of cases with similar markings.

 

[m&p45acp10+1]

Most semiauto ammo is dirty. It is going to be sooty. Some will shoot a little less sooty than others. If dirty clean it. There are a ton of ways to clean the brass. For pistol brass unless it is ultra cruddy from being in the bucket with mud I do not worry about cleaning it. They shoot just the same.