Carbon build up on brass shoulders

[Gregor.Samsa]

Today I noticed more carbon accumulation on the shoulders of my brass than usual. It seems as if more gas may be leaking around the neck than optimal. No other issues, the loads were accurate and consistent. The picture is somewhat lousy, the carbon was more evident in person. Is there anything to this? Thanks

 

[FCS]

Gas gun?
Bolt gun?
Virgin brass?
10x fired brass?
Powder & bullet used?
Suppressed or unsuppressed?

 

[Gregor.Samsa]

Bolt gun- tikka ctr
Second firing on brass, FL sized, mandrel expanded
H4350
140eldm
Unsuppressed

thanks

 

[Smittiac]

How much are you bumping the shoulder when sizing?

 

[Gregor.Samsa]

How much are you bumping the shoulder when sizing?

0.002”
Thanks

 

[Gee Kay]

how many rounds down the barrel?
grab a torch (in aussie), light everywhere else and have a look down the receiver just in case it needs cleaning.
what comes out the case ends up in the receiver/barrel where the case once was.

 

[Gregor.Samsa]

how many rounds down the barrel?
grab a torch (in aussie), light everywhere else and have a look down the receiver just in case it needs cleaning.
what comes out the case ends up in the receiver/barrel where the case once was.

900ish rounds

 

[Smittiac]

Give the old girl a serious scrubbin and you're still getting sooty brass?

 

[918v]

Today I noticed more carbon accumulation on the shoulders of my brass than usual. It seems as if more gas may be leaking around the neck than optimal. No other issues, the loads were accurate and consistent. The picture is somewhat lousy, the carbon was more evident in person. Is there anything to this? Thanks

Maybe your load is too mild. And it’s been cold outside lately.

 

[Gregor.Samsa]

Maybe your load is too mild. And it’s been cold outside lately.

I actually bumped my load up from 41.5 grains h4350 to 42.2. The 41.5 load was developed at 95-100 degrees I shot the 42.2 yesterday at 50 degrees. They chonoed the same speed at 2700fps. I was able to get much higher velocities using rl16 but had very good accuracy at this speed and it seems like it will be easier on the barrel etc. thanks

 

[FCS]

Annealing brass?

 

[Milo 2.5]

I would clean the chamber real good, esp shoulder area. Your .002" bump after first firing may be your culprit, brass not close to chamber length.

 

[1moaoff]

This ☝ possibly

 

[Gregor.Samsa]

Annealing brass?

I do anneal but these cases were not annealed

 

[Gregor.Samsa]

I’ll give the chamber a good scrub and try bumping .001 and see if that does anything. Thanks for the advice.

 

[Smittiac]

Don't bump until you strip the bolt and see if they chamber without pressure.

 

[FCS]

I do anneal but these cases were not annealed

Try annealed cases, see if carbon foul the same.
Might be as simple as that load in once fired brass w/o annealing is enough to prevent seal neck / shoulder, cause increased carbon fouling.

 

[Gregor.Samsa]

Don't bump until you strip the bolt and see if they chamber without pressure.

I ca do this with one of the spent cases correct? Or should I size but not bump?

 

[Smittiac]

Spent case shouldn't fit without pressure correct. Size but no bump shouldn't fit, if it does it means they haven't full expanded in the chamber. If that is the case, load em up with no bump go shoot again rinse and repeat.

 

[Milo 2.5]

One other thing to do would be to measure the neck of a loaded rd, and the neck of a fired case and try figure how much it is expanding when fired. I had a shit show with a couple dashers that were chambered with a tapered neck reamer, using hydro formed brass. To resolve gas coming back, I had to impart somewhat of a goiter on the neck to shut it off.