Soot Covered Cases

[fx77]

308 rifle . Very accurate 3 lug BAT action. Standard chamber not a tight neck
Yesterday at the range the shooter next to me said he was a cloud of smoke as I fired.
Normally the case has carbon deposited on the neck but not the case body. The case was covered in carbon .
The cases are lapua, VV N 135 with 155.5 Gr Berger. Groups are in the 1-2's range. The bullet is .015 from the jam. The neck is skim turned, and measures .015 thickness. FL die with .004 tension on the necks.
All neck are annealed after each firing. Resizing is 1.5 Thou and loaded and fired case measurements verified this degree of FL resizing.

The adjacent shooter suggested I try one of his Federal Gold Medal Match factory cartridges. I found that the accuracy was fine, and only the neck and shoulder had carbon ( i.e. burned powder) deposited. The body of the case was still quite clean in comparison.

My accuracy is therefore fine, but am at a loss to see why the bodies are so soot covered.

My Cases have> 20 firings with no neck issue or loose primers on inspection after firing.

Therefore my question is why is there so much soot on the cases below the neck .
Do you think it is just because the cases are old?

 

[Rockchuck]

I think so sounds like there work hardened

 

[Ned Ludd]

It doesn't sound like work-hardening is necessarily the most likely cause if the cases were properly annealed after every firing as the OP noted. Certainly >20 firings on the brass is getting up there, but not unheard of by any stretch. Did the adjacent shooter notice the same cloud of smoke when you fired the FGMM rounds? Can you post pictures of the two different fired cases (i.e. yours and the FGMM)? Were there any other obvious visual differences in the two fired cases other than carbon deposits?

 

[fx77]

Oops too late on the cases. Discarded them ,and did not take pics.
that is because I thought I could bet answers locally. But with that I was unsuccessful
so i posted on the forum for other opinions.
No cloud of smoke on the FGM was noted.
No other visual differences. I measured my fired and unfired cases and they were within spec.
I did not have a pre-firing measurement of the FGMM case.

 

[Dusty Stevens]

I dont think n135 is the right powder for that

 

[243winxb]

Increase the powder charge closer to 40 grs.

Seat full diameter of bullet shank to case neck shoulder junction, for a better burn.

Use a bushing die & size only 1/2 of the necks. After a few firings, the unsized part will seal.

https://forum.accurateshooter.com/threads/berger-155-5-gr-fullbore-jump-tolerence.3936266/

 

[fx77]

I dont think n135 is the right powder for that

Load came from VV reloading manual

 

[Sleepyhollow]

Had this issue in a ppc lately. My scale was showing 30.0 grains. Every case had blow by on it. Long story short My florescent lights was affecting my scale. I put led lights in my loading room and recalibrate my scale. Low and be hold my scale was showing 30.0 grs but actually throwing 26.6. IE to light a load and chamber was not sealing. And I never anneal. Fix the issue

 

[FeMan]

I think Dusty is correct. I ran that combo in Quickload and the chamber pressure is less than 45k psi at 103% fill (40.5 grains). I am betting its the combination of old brass that has slowly hardened and not enough chamber pressure to create a seal that is causing your issue, and a powder change to something capable of achieving pressure closer to SAAMI will cure the issue.

 

[fx77]

Had this issue in a ppc lately. My scale was showing 30.0 grains. Every case had blow by on it. Long story short My florescent lights was affecting my scale. I put led lights in my loading room and recalibrate my scale. Low and be hold my scale was showing 30.0 grs but actually throwing 26.6. IE to light a load and chamber was not sealing. And I never anneal. Fix the issue

I have LED's over the bench. Checked load in grains on a second scale

 

[243winxb]

Lapua small primer?

 

[fx77]

Lapua small primer?

Federal Match small rifle primer

 

[243winxb]

chamber pressure is less than 45k psi

Cartridge Brass-
Material is 70 copper/30 zinc with trace amounts of lead & iron , called C26000. Material starts to yield at 15,000 PSI when soft (annealed), and 63,000 PSI when hard.
Material yields, but continues to get stronger up to 47,000 PSI when soft, and 76,000 PSI when work hardened.

Neck/shoulder has been annealed, but maybe not correctly? Sorry.

 

[243winxb]

Federal Match small rifle primer

Found problem. imo. Smaller flash hole too?

 

[fx77]

Found problem. imo. Smaller flash hole too?

My error --Federal Match LARGE primer... so sorry

 

[fx77]

Cartridge Brass-
Material is 70 copper/30 zinc with trace amounts of lead & iron , called C26000. Material starts to yield at 15,000 PSI when soft (annealed), and 63,000 PSI when hard.
Material yields, but continues to get stronger up to 47,000 PSI when soft, and 76,000 PSI when work hardened.

Neck/shoulder has been annealed, but maybe not correctly? Sorry.

Annealed on AMP annealer using their program's recommendation

 

[243winxb]

I think the COL needs to be known. Where is the shank of the bullet sitting.

At .004" neck tension, should be plenty.

FL die with .004 tension on the necks.

 

[fx77]

Bullet is seated .015 from "jam"

 

[243winxb]

Soot is caused by low pressure, as said above. I am out of guesses.

 

[762willdo]

How much are you bumping them when re-sizing?