Carbon on shoulder/neck of fired case

[bsumoba]

Just curious...

I have seen cases where the carbon on a fired case only resides on the neck portion of the case.

But, I have seen cases where the the carbon will go all the way down, about half way on shoulder. To me, this might indicate an "improper seal" on the case, thus allowing blowback of carbon onto the shoulder of the fired case.

I cannot see a difference between the two on paper for score or group size, so it appears to not make a difference.

I am curious as to your thoughts on why this happens.

 

[Dusty Stevens]

Sometimes a 2lug action will have 2 stripes going down the shoulder and a 3lug will have 3.

 

[Texas10]

Time to anneal.

 

[Eraser]

Sometimes a 2lug action will have 2 stripes going down the shoulder and a 3lug will have 3.

Are you serious?

 

[JMayo]

Light loads, lack of seal at shoulder maybe.
Happens with pistols I know.

 

[260 Ravage]

A mild load and a need for annealing will definitely force soot back on the case. I am with Texas10: time to anneal.
Also, I am all In with Dusty with the lug theory. Yes, he is serious.

 

[avidflyer]

I anneal everytime with a amp and use a raft load of varget and still get it on the necks....308.

 

[Pigdog]

I anneal everytime with a amp and use a raft load of varget and still get it on the necks....308.

I also anneal every time with my 6.5x47L cases and get soot on neck and shoulder. Its about 50% of cases where it goes on neck and shoulder for me and about 50% on neck only. So I don't think its related to annealing.

 

[stifffingers]

I anneal everytime with a amp and use a raft load of varget and still get it on the necks....308.

You can also get carbon all the way back to the case head if you are shooting short bullets in long throated chambers. The bullet leaves the case and hasn't made the seal in the barrel yet.

 

[ClassCat]

Are you serious?

Yes he is, They look like peaks and valleys, usually on hotter loads.

 

[ClassCat]

Just curious...

I have seen cases where the carbon on a fired case only resides on the neck portion of the case.

But, I have seen cases where the the carbon will go all the way down, about half way on shoulder. To me, this might indicate an "improper seal" on the case, thus allowing blowback of carbon onto the shoulder of the fired case.

I cannot see a difference between the two on paper for score or group size, so it appears to not make a difference.

I am curious as to your thoughts on why this happens.

A couple of questions, How much are you bumping the shoulder, and what is the chamber dimension and the neck size on a loaded round ? Sounds like you're getting blow by on a loose fit.

 

[bsumoba]

bumping 0.002. annealing every time.

.317 neck. .3125 loaded round. pretty standard 284 dimensions.

A couple of questions, How much are you bumping the shoulder, and what is the chamber dimension and the neck size on a loaded round ? Sounds like you're getting blow by on a loose fit.

 

[ClassCat]

bumping 0.002. annealing every time.

.317 neck. .3125 loaded round. pretty standard 284 dimensions.

You have .0045 clearance on a loaded round, that may be the problem. Has this started since the outside temperature has risen ?

 

[avidflyer]

You have .0045 clearance on a loaded round, that may be the problem. Has this started since the outside temperature has risen ?

284 guys swear at a 5k neck.... i always thought that was much but with the 284 pretty common

 

[ClassCat]

284 guys swear at a 5k neck.... i always thought that was much but with the 284 pretty common

Not disputing the neck size. I shoot a .2596 on a .262 chamber and still get a little carbon on the neck. None on the shoulder though.

 

[Bart B.]

There is rarely enough pressure in the case behind the bullet to seal the case neck against the chamber neck, so powder residue on necks is normal. Peak pressure happens when bullets are a few inches down the bore, there's nothing preventing it from pushing powder residue back onto the case neck that is not sealed against the chamber neck wall. A couple to a few thousand psi will push the bullet clear of the case mouth well into the rifling.

The firing pin drives the rimless bottleneck case shoulder hard against the chamber shoulder sealing the gas fairly well at that point as pressure in the case builds..

 

[Dusty Stevens]

The firing pin drives the rimless bottleneck case shoulder hard against the chamber shoulder sealing the gas fairly well at that point as pressure in the case builds..

On all my rifles the extractor holds the case against the boltface. No wild shifting going on with my properly sized cases even if there is slack in the extractor

 

[Bart B.]

On all my rifles the extractor holds the case against the boltface. No wild shifting going on with my properly sized cases even if there is slack in the extractor

Interesting indeed. Please enlighten me.

What actions do that? What's slack in extractors?

What mechanics pull or push the extractor claws against chambered case rims to hold case heads against bolt faces that withstand the 25 to 30 pound firing pin force?

 

[Milo 2.0]

Interesting indeed. Please enlighten me.

What actions do that? What's slack in extractors?

What mechanics pull or push the extractor claws against chambered case rims to do hold case heads against bolt faces that withstand the 25 to 30 pound firing pin force?

The claw type on a Mausingfield will hold a case, don't ask how I know.

 

[Bart B.]

The claw type on a Mausingfield will hold a case, don't ask how I know.

Just looked at their bolt parts diagram and saw nothing to force case heads against bolt faces.

The extractor claw pushes the case rim sideways against the bolt face shroud to hold the case during bolt opening until the ejector pushes it out.

Remove the cocked bolt then slide a case head into it. How much clearance is there between bolt face and case head with the extractor pushed back as far as possible?