Carbon on the outside of the case neck after firing?

[KiloTango]

In the different loads I've tested, the most accurate at 100 yards leaves carbon around the necks of fired cases(ie almost black). A slightly hotter load I found more accurate at 600 yards leaves much less carbon on the case necks(some slight carbon deposits).
Additional info:
6.5x47
130gr Bergers
H4350
39.0gr yields 1/4-1/3moa at 100, and 2" vertical by 5" horizontal 10 shot groups in light variable winds.
39.7gr yields 1/2-3/4moa at 100, and 1" vertical by 3.5" horizontal 10 shot groups in the same winds.
The carbon around the necks never goes past the necks. I had read somewhere that carbon around the necks is a sign of low pressures? The 39.7gr of H4350 is a max load in Berger's manual...I had tried a load at 40.0gr with no pressure signs when I was developing a load at 100 yards, but did not check how much carbon was around the necks...is this something I should be worried about?
Thanks,
Ken

 

[Bullet bumper]

It's not a big concern if it's only minor carbon .
Low pressure is not always the reason.
Uneven or rough neck walls can do it .
I think uneven neck hardness may contribute also.
Make sure the inside of the chamber neck area is clean and no carbon ring present .
A light skim 70% neck turn and an anneal may help .
I skim neck turn every cartridge I load for and never ever get carbon on the necks .
The powder could be a bit slow for the application . Try Varget .

 

[BrentM]

I always get carboned necks. I shoot lapau brass, neck sized, fire formed, and nothing changes it. I have loads that produced sticky bolt lift, flat primers, and extractor marked, still carboned up. So the pressure was definitely there.

I hate it, but the rifle shoots well so I don't bother to change anything. I thought it might be dirty burning powder but 4350 is not typically described as dirty and you have the issue, so who knows.

 

[varmintH8R]

I have two rifles that consistently leave some amount of carbon on the necks (different bullets, powder, etc and its still there). Unless it is excessive, I don't sweat it.

 

[Mikecr]

Sounds like excess trimming from chamber end.

 

[varmintH8R]

Sounds like excess trimming from chamber end.

Never considered that. I'll bet it is. Trim-to-length is likely waaaay shorter than necessary in my rifles that leave carbon.

 

[KiloTango]

So I'm trimming to the recommended 1.840", I know the chamber will be 1.850", should I not be trimming this short?
Thanks,
Ken

 

[varmintH8R]

So I'm trimming to the recommended 1.840", I know the chamber will be 1.850", should I not be trimming this short?
Thanks,
Ken

I think Sinclair makes inserts so you can measure your true chamber length. I have enough reloading OCD to not add this to my list. Unless, of course, someone can show me the errors of my ways or convince me I can get 0.05" of additional accuracy...

 

[Bullet bumper]

Most chambers have about .015 more room for the neck length than the length of a new case anyway. You can't get a much shorter neck than a .223 Rem and I don't get any carbon on my necks .
Just because the total pressure shown on the primers and felt on the bolt lift is up there does not mean the pressure curve was quick enough to get the case neck sealed before the powder really starts to burn to full pressure further down the barrel .
With slow burning powders the bullet is pushed into the start of the bore by a column of unburnt powder and at that point the pressure may be low and not enough to seal a hard case neck . A microsecond later the full pressure develops but some carbon gases may have already infiltrated through the unburnt powder grains and slipped past the neck , a microsecond later it seals.
Try working up a load for Varget it's faster and see if that helps .
I have noticed a pattern of Americans using slower powders than is best in lots of cartridges. Our powder manufacture ADI dropped one of our best powders for 223 in favour of a slower powder that suited the Hogdon USA market and it was not the best powder at all . I think it's encouraged by the US firearms industry as a safety measure because it's harder to overload with slow for the cartridge powders and it's starting here also .

 

[BrentM]

All could be accurate and true. However, I am the Honey Badger on this one. My rifle shoots faster, more accurately, and is consistent with a slow burning powder. If the payment is a little of carbon that does no harm, so be it. My cases are at max length according the Berger manual. I trimmed my lapau brass to the shortest case in the lot and checked them after fire forming.

I think the guestions that would concern me more are: does the carbon get into the shoulder? Does this carbon issue create problems for the rifle itself?

I am wondering if my recent pressure signs are more from a carbon build up in the rifle around the neck area vs work hardened case necks. I just annealed those last night and loaded a batch of 50 for next weeks hunt. Tonight I think I will work on cleaning the rifle thoroughly for carbon.

 

[Max Heat]

With my S110 in 7RM (factory bbl), I see burn sign on the outside of the necks of fired cases. But it does not go all of the way around. It covers only about 1/3 of the way around the neck. Am I correct to assume that is most likely the result of a slight chamber-to-bore mis-alignment?

 

[Mikecr]

I strive for low ES in my reloading plan.
With this there are a few adjustments from common:
-Fastest appropriate powder -that fills a case
-Best performing primer and best primer striking
-Long enough barrel for powder burn
-Matched reloaded case H20 capacities
-Smallest neck clearances practical
-Tightest chamber end to trim clearance practical
-Consistent neck tension

With testing in the past I could call a hit to ES with a look at neck sooting, before checking the chrono. And I eventually managed it with more consideration of clearances left with trim length.
Less chamber end clearance meant less sooting, meant less ES with my cartridges & loads.
This was an easy adjustment for me because 'matched reloaded case H20 capacities' took me away from FL sizing, which took me away from chasing trim lengths anyway.
I started setting the fireformed chamber end clearance as close as I could, while not under 5thou, and a little bit of trimmed neck length variance from this(~5thou) did not matter to ES.

Being this close I still look as a habit for any shine to mouths on ejection. This is a sign I'm getting carbon buildup from chamber end(time to clean), or the brass has stretched to chamber end(which is dangerous).
Now & then I see the carbon sign, but I haven't had to actually re-trim necks yet.

It's just one factor, but no matter the cartridge or load, I wouldn't act on generalizations about it.
It's like most anything, you should do as well as practical with it.

 

[Bullet bumper]

All could be accurate and true. However, I am the Honey Badger on this one. My rifle shoots faster, more accurately, and is consistent with a slow burning powder. If the payment is a little of carbon that does no harm, so be it. My cases are at max length according the Berger manual. I trimmed my lapau brass to the shortest case in the lot and checked them after fire forming.

I think the guestions that would concern me more are: does the carbon get into the shoulder? Does this carbon issue create problems for the rifle itself?

I am wondering if my recent pressure signs are more from a carbon build up in the rifle around the neck area vs work hardened case necks. I just annealed those last night and loaded a batch of 50 for next weeks hunt. Tonight I think I will work on cleaning the rifle thoroughly for carbon.

The Berger manual like any other manual will only quote SAAMI case length specs not how long your actual chamber is in the neck area . Most reamers and hammer forging mandrels are made to give extra clearance over and above those standard case neck lengths . You really have to measure what you have in your gun and work from there . Like Mikecr does .
I agree sometimes the gun shoots best with a slower powder in a certain load and there's not much else you can do.