Carbon on shoulder/neck of fired case

[Milo 2.0]

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?

I really could give a rats ass, I shoot guns, not try figure them out. This case would have never fired in a Rem 700, that I'd bet a substantial amount of money on.
This was a pretty simple thread till you got yourself involved. I'd like to know how you figure the force from a firing pin will pin the shoulder of a case tight enough to seal anything off. You should let some of your theories rest, I'm not seeing a lot of buy in on most of them.

 

[Milo 2.0]

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.

I've had this happen a couple times, and I'm not getting into my specifics. But it is definitely not sealing off for some reason. Sometimes more powder will fix it, if allowable.
I do know this, if you have carbon on the necks of your brass, you also have carbon on the shoulder of your chamber and the more you shoot w/o cleaning the chamber, the more your problem will compound itself.

 

[Eraser]

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

I understand the carbon on the neck thing. I just can't grasp how the number of bolt lugs effects the carbon pattern.

 

[ClassCat]

I understand the carbon on the neck thing. I just can't grasp how the number of bolt lugs effects the carbon pattern.

To be honest with you i don't get it either, but its there, and not a coincidence. IMHO it is from the 60,000 psi plus or minus, of a PPC pushing the bolt back ever so slightly. Some that are smarter than i am say it is not the lugs itself, but the area between the lugs that the valleys appear on the case neck. it almost looks like a graph on the case neck.

 

[Bart B.]

I'd like to know how you figure the force from a firing pin will pin the shoulder of a case tight enough to seal anything off.

No powder residue on shoulders except for reduced loads.

You should let some of your theories rest, I'm not seeing a lot of buy in on most of them.

I see a lot of buy in all of them.

 

[pirate ammo]

To be honest with you i don't get it either, but its there, and not a coincidence. IMHO it is from the 60,000 psi plus or minus, of a PPC pushing the bolt back ever so slightly. Some that are smarter than i am say it is not the lugs itself, but the area between the lugs that the valleys appear on the case neck. it almost looks like a graph on the case neck.

with a 9 lug 788 you still pick up some,,but not much in mine,,

 

[Dusty Stevens]

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?

How much force does it take to tear a rim off a case? More than 25-30lb im sure and ive seen every extractor design out there tear one off

 

[Dusty Stevens]

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?

I remember even guffey calling you out on this. A firing pin doesnt make a case jump the extractor then expand upon firing back past it. That picture posted above is a perfect example

 

[Bart B.]

I remember even guffey calling you out on this. A firing pin doesnt make a case jump the extractor then expand upon firing back past it. That picture posted above is a perfect example

I've seen that happen with 308 win ammo fired in 30-06 chambers. Normal with a few tenths inch shoulder clearance.

What about either of those cartridges fired in their regular chambers with .003" head clearance? Is that clearance reduced to zero by extractors before they fire?

Ps:
corrected "cases" to "chambers."

I've never claimed a case jumped the extractor. Frank Guffey once claimed I did but never offered proof. He got upset 'cause I claimed rimless case shoulders can be set back by firing pin impact on primers and thought a case had to jump the extractor to do that; or some such thoughts.

 

[Dusty Stevens]

Probably not .002 or .003- thats where the slack comes in i spoke of. Some have more than others and every case is different

 

[pirate ammo]

I've seen that happen with 308 win ammo fired in 30-06 cases

do you really mean CASES,bullets are both 30 cal,,or do really mean CHAMBERS,,I may not be the sharpest here but I do know the difference between CASES and CHAMBERS,,

 

[gunsandgunsmithing]

To the op...This is fairly common with light loads and/or too slow a powder. If the fp pressure were enough to prevent it, it'd virtually never happen, but it does, when loads are too light or powder too slow.

 

[500Stroker]

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

+1^^^^^^^^^
6BRX, varget and custom dies
I dont think it makes a difference, see attachment.

 

[Bart B.]

do you really mean CASES,bullets are both 30 cal,,or do really mean CHAMBERS,,I may not be the sharpest here but I do know the difference between CASES and CHAMBERS,,

So do I know the difference so I corrected my error in that post.

Thanks for the alert.

 

[newbieshooter]

I shoot a 6BR that results in carbon down the shoulders. Cases are annealed each time. It shoots really well - so I've kept the same load.

 

[Bart B.]

Probably not .002 or .003- thats where the slack comes in i spoke of. Some have more than others and every case is different

I agree.

Across several action makers, with each and every one, with the extractor pushed back as far as possible, there's a few to several thousandths clearance between bolt face to extractor lip/claw to the case rim. Rim thickness is always less than bolt face to claw/lip.

Physically impossible for extractors to pull case heads against bolt faces on every action checked.

How do some loads end up with primers backed out several thousandths from case heads they're held against bolt faces?

 

[pirate ammo]

severan

new word,fix your fingers,,

 

[Bart B.]

How much force does it take to tear a rim off a case? More than 25-30lb im sure and ive seen every extractor design out there tear one off

M1 Garand, Win 70, Mauser 98 and M1903 extractors have held 308 Win case heads in place (not against bolt faces, just close) while the round fired in 30-06 chambers, they didn't break. These I've seen, mostly with Garands

new word,fix your fingers,,

Fixed.

 

[calgarycanada]

In my experience light load, work hardened cases or shoulder set back too far or slower powder(for given cartridge) or combination of those can cause it.