Carbon on shoulder

[1raggedhole]

When I full length sized new brass and fired the first time, brass only had small amount of carbon on the neck as shown on the right. After a few firings, and now only bumping the shoulder back 0.001-0.002", they always come out with carbon down on the shoulder like the left case. Nothing else changed. 105 amax, 0.004" jump, 29.8 gr varget, cci 450. Most concerning is that the groups aren't as small now when carbon is on the shoulder. Any ideas?

 

[dkhunt14]

Brass needs annealed. It got harder and is not sealing in the chamber. That and neck tension is causing bigger groups. Matt

 

[spclark]

Dkhunt14 has a point about annealing but I'd expand on it a bit by suggesting you may want to boost your load a bit so necks expand a little faster upon firing.

Clean necks fired in a clean chamber will show carbon on shoulders & sometimes case body if the load's on the low side of what it'd otherwise take to get good gas sealing.

What 6mm cartridge are you shooting that load in? Factory (generous chamber neck clearance) or custom-fitted (maybe not so generous?) barrel?

It all matters....

 

[SS427]

I've noticed the same thing recently with one of my .223s, but I suspect it was because it is a lighter load shot at near freezing temps. I'm waiting to see what happens when I go shooting in temps a little higher before I conclude anything. I suspect a hotter charge would make the problem go away.

 

[1raggedhole]

Dkhunt14 has a point about annealing but I'd expand on it a bit by suggesting you may want to boost your load a bit so necks expand a little faster upon firing.

Clean necks fired in a clean chamber will show carbon on shoulders & sometimes case body if the load's on the low side of what it'd otherwise take to get good gas sealing.

What 6mm cartridge are you shooting that load in? Factory (generous chamber neck clearance) or custom-fitted (maybe not so generous?) barrel?

It all matters....

6BR, criterion barrel with 0.272" neck, Lapua brass (fired about 3 times)

 

[M-61]

If this is a bolt action have you tried NOT bumping the shoulder? Were you bumping because of difficulty chambering the round?

 

[1raggedhole]

If this is a bolt action have you tried NOT bumping the shoulder? Were you bumping because of difficulty chambering the round?

No.

 

[M-61]

No.

"NO" to BOTH questions?

 

[savagedasher]

Just anneal it like dkhunt said Larry

 

[LHSmith]

View attachment 1002129 When I full length sized new brass

Don't do this. Double check your FL die setting procedure.

 

[1shot]

Don't do this. Double check your FL die setting procedure.

I would say, double check your bump measurement with a reliable bump/datum gauge. My guess is you are setting the shoulder back more than you think. An inexpensive gauge can be made from a piece of scrap barrel and your reamer for that cartridge.
I hope this helps,

Lloyd

 

[Patch700]

Gotta go with dkhunt and Larry here.. Last time I had this problem was with a 6.5x284 using Nosler brass that was only once fired. Believe me , going up on the powder charge wasn't going to fix it.. But annealing sure did.

Tossed the nosler brass after the next loading when the good stuff from finland showed up.

Good luck.

 

[bblackwell]

I had that carbon problem on my Dasher last year. Took me forever to figure it out. The FL die that I was using was bumping the shoulder back at the wrong angle. I changed to a different FL die and they sealed off with a nice solid line around the neck...........

Lot of good suggestions here especially the one about annealing.

 

[newbieshooter]

I also have carbon on shoulders when shooting my 6BR. Cases are annealed after each firing and cases are FL sized with shoulders bumped .0015 (cause it is hard to close the bolt unless I do this step).

Are there any negatives in shooting with a load that produces carbon on the shoulders? The groups are really good - so just ignore the carbon on the shoulders and keep shooting it that way?

 

[dkhunt14]

I also have carbon on shoulders when shooting my 6BR. Cases are annealed after each firing and cases are FL sized with shoulders bumped .0015 (cause it is hard to close the bolt unless I do this step).

Are there any negatives in shooting with a load that produces carbon on the shoulders? The groups are really good - so just ignore the carbon on the shoulders and keep shooting it that way?

You need to clean the neck and shoulder area of the chamber or you can get a carbon buildup. If properly annealed you should not get much on the shoulders. Do you check bolt closure with the fire control out the bolt? If not you cant feel it right. Matt

 

[newbieshooter]

You need to clean the neck and shoulder area of the chamber or you can get a carbon buildup. If properly annealed you should not get much on the shoulders. Do you check bolt closure with the fire control out the bolt? If not you cant feel it right. Matt

Thanks Matt. I try to clean neck/shoulder/chamber the best I can after each range trip.

I anneal the cases (time established using tempilaq 750) the same each time. Using these same annealed/FL sized cases - I do notice that if I increase the powder charge by .8 grains, I get fired cases with no carbon on the shoulders - but the groups aren't as good. So I just continue to shoot with the lower charge and just clean the best I can. Or would you recommend trying to find a higher powder charge that shoots great - and doesn't leave carbon on the shoulders?

 

[dkhunt14]

What doesn't make sense is the first firing doesn't show it but the more fired cases do. That's why I think it is annealing. Matt