Carbon/soot on Case Shoulders

[lawrence97]

i only speak from my mistakes, so.... i had length trimmed some brass and deburred the neck with one of those cheesy lee thimble tools. i got sloppy, or the tool quit cutting cleanly, and i pushed down a burr that really could only be seen under a magnifying glass. upon firing the burr flattened out but.... it was not fully around the neck, being more pronounced on one side usually.

i posted a photo quite some time back and i think it was on a very similar thread as yours.

When I trim I use a giraud so no rough edges on my brass.

 

[lawrence97]

Lawrence, a different angle…. How do you clean your chamber? Any carbon build up in the chamber? Any wet residue remaining after the clean in the chamber? How do you clean the brass? Anything on it that carbonises on the case? Some long shots there……

An observation would be that the shoulder angles in that first pic looks very different to each other…..

Sorry, one more….. can you drop a projectile into the neck of a fired case? Or is it a tight fit?

Depending on round count more often on the 6bra I use solvent and some iosso or kg2 bore finish. I use a borescope to verify results.

 

[lawrence97]

I think virgin brass is stronger with the most neck tension, I would set a few brass aside without annealing and add some NT for comparison

I’m gonna try some of my 284 brass that’s been turned for a .313 neck. I already tried some brass that was neck turned for my .268 6bra and it sealed properly. I suspect the necks are thick when left as a no turn. I was just wondering if others running no turn chambers have the same experience.

 

[LCazador]

I’m gonna try some of my 284 brass that’s been turned for a .313 neck. I already tried some brass that was neck turned for my .268 6bra and it sealed properly. I suspect the necks are thick when left as a no turn. I was just wondering if others running no turn chambers have the same experience.

Once you fireform there should a difference in water capacity. There is more water capacity in the fireform cases therefore reducing the pressure and allowing the gas to pass by. Have you tried increasing bullet tension by trying different bushing sizes? Try tighter bushings in .001" increments to +.005".

 

[Dusty Stevens]

You need a snappier powder pressure curve. Or just keep on shooting.

 

[lawrence97]

You need a snappier powder pressure curve. Or just keep on shooting.

But if that were the case why isn’t the virgin brass reacting the same? It also has to grow in more areas than the once fired stuff that only gets sized down .002 in the critical areas.
The powders being used are the most common per caliber and the velocities are inline with the speeds were most tune at.

 

[old_heli_logger]

Virgin brass doesn't have any sizing lube on it. Are you sure it's soot from powder burn?

 

[spudgun]

WOW, I was going to post about the same thing. My 6.5 CM was getting some blowby and I showed another shooter my brass.

He suggested that I needed to anneal the brass.

The brass I have been using is Starline and I have been loading this same 150 pieces for 4 years now.

Today I decided to try to anneal some and see if that took care of my issues.

I watched a youtube video of a guy using a propane torch and a electric drill.

I tried his second way of doing it and it worked. Loaded up 6 rounds of annealed brass and went to the range.

The picture below shows 12 pieces of my brass that I shot today. the top are not annealed and the bottom 6 were annealed.

You can see the differance on the soot deposit.

 

[243winxb]

Now, THIS is a soot problem.

 

[jelenko]

WOW, I was going to post about the same thing. My 6.5 CM was getting some blowby and I showed another shooter my brass.

He suggested that I needed to anneal the brass.

The brass I have been using is Starline and I have been loading this same 150 pieces for 4 years now.

Today I decided to try to anneal some and see if that took care of my issues.

I watched a youtube video of a guy using a propane torch and a electric drill.

I tried his second way of doing it and it worked. Loaded up 6 rounds of annealed brass and went to the range.

The picture below shows 12 pieces of my brass that I shot today. the top are not annealed and the bottom 6 were annealed.

You can see the differance on the soot deposit.

Maybe just the pic, but the cases on the bottom look sootier than the ones on the top.

 

[Tod Hendricks]

Hey Lawrence,

I’ve dealt with this exact issue for quite a while. For my situation I think it’s related to the chamber, I’m not sure why, but it only happens with one reamer.

I put a more aggressive cross hatch (180 emery) in those chambers and even the neck area. For me it helped a lot.

On a side note, it amazes me when I have soot down the case and don’t see any effect on target at LR.

Tod

 

[spudgun]

Maybe just the pic, but the cases on the bottom look sootier than the ones on the top.

I was refering to the soot on the shoulders. The cases do look dirtier after annealing due to the brass discoloration but I think it softened the brass so it expands and gets a better seal on the shoulder areas.

 

[Kracken McGraw]

I was refering to the soot on the shoulders. The cases do look dirtier after annealing due to the brass discoloration but I think it softened the brass so it expands and gets a better seal on the shoulder areas.

Looks like your having great luck with the Starline brass. How many firings do you have on that four year old brass?

 

[JMayo]

My 6bra seals at sholder.
30 br seals at case mouth.

The older the brass got (could have been the more rounds on that barrel) the further it came down on sholder.

One of my annealer torches now point lower toward sholder.

Most bra's don't grow much.

 

[spudgun]

Looks like your having great luck with the Starline brass. How many firings do you have on that four year old brass?

Too many to count.

Out of 150 cases I think I have discarded maybe 15 for split neck and 4 for primer pockets (small rifle primer)

During the summer I shoot 600 and 1000 yd every week, so maybe 75-100 reloads.

I was using Federal and could only get maybe 5 reloads before I go neck splits.

 

[jsthntn247]

I had the same issue with a 7 ss. Funny thing was it only had .002 clearance in the neck at first when the blow by was occurring. It would soot every time and I tried all the same things you did. I turned the necks for .005 clearance and now it seals at the neck, no more blow by with the same brass prep. I’m guessing that firing the brass after the necks are turned flows some brass and causes a small buildup at the base of the neck. This buildup of brass is now sealing the chamber. I had a 7-08 with .012 neck clearance and would blow by soot to the bolt face. Turning that brass also fixed it.

 

[Dave M.]

The virgin brass being softer is my thought also but I took a few pieces of brass and annealed to a glowing red neck and those still had soot on the shoulder. I would think annealing that much would have made it as soft or softer than the virgin brass ever was.

Glowing red neck is far too hot. You were not testing what you were trying to test with those pieces.

 

[lawrence97]

Glowing red neck is far too hot. You were not testing what you were trying to test with those pieces.

Well I tried my regular annealing and took it to an extreme for testing purposes. Annealing or not doesn’t seem to make a difference for soot on the shoulder.

 

[Shanedogg]

Now, THIS is a soot problem.

I've had this happen on every 257 bee barrel I've had. 5, 2 factory. Only variable I can chalk it up too is cleaning or lack of and free bore... Following this one....

 

[chootem]

I have exhausted all attempts at trying to solve the soot on shoulder issue. I am getting the soot on Alpha 6BRA brass as well as on my 284 Winchester using Lapua 284W brass. I typically use a .268 neck on my 6mm’s and a .313 on my 7mm’s and never experienced this.

The problem exists on my NO turn chambers and what is odd is that the virgin brass seals just fine. The soot appears after resizing on the second firing.

Most would say:

1-Your running low pressure but not in my case. My 6bra is running 2900-2920 using Varget/h4895 and Sierra 107 or Berger 108’s. My 284w w a 28” barrel is pushing Berger 180’s 2760-2790 using h4350 and h4831sc.

2- You have excessive headspace and are bumping the shoulders too much…. Well I only bump .002-.003 as measured with firing pin removed and to allow the bolt to drop closed freely. I did try sizing .005-.001 but I got some resistance on closure and on opening of the bolt and the soot was still present on the shoulder.

3- You need to anneal more aggressively….. I got my 6bra and 284w brass glowing red at the neck to perform the test and the soot still there.

4- Your die isn’t compatible with your chamber. For the 6bra I used a Harrell’s and a whidden die with the same results. With the 284, the body shoulder junction on virgin brass measures .473”, fired brass is .478” and resized is .476”.

5- You have insufficient neck tension. I used an arbor press with seating pressure gauge. Usually 20-40psi is where I am at with .002 neck tension. I also tried in the 40-60psi range and some of my 284 was registering over 90psi and none of this made a difference.

6- Your chamber neck is over sized. My no turn 6bra is a .274 and my 284 is a .319. My loaded 6bra is .269 and loaded 284 is .314. Virgin brass does not exhibit the soot on the shoulder.

7- I did test some of my brass that was neck turned for a .268 chamber. This brass was .265 loaded and it did seal when I fired it in the .274 no turn chamber. The whole point of the No turn is to not have to neck turn!

As for accuracy at 600 yards both are performing with excellent results in an fclass setting(2.5”-3.4” 15 shot groups and vertical is in the 1”-2.4” range). My chrono numbers with the 284 are nice and low. The 6bra has some higher ES/SD but it’s shooting very good. My .268 6bra had some very tight chrono numbers but it did not shoot any better than my NO turn. For 600 yds I am not too worried about what the chrono is telling me.

Any suggestions or something I might be overlooking?

View attachment 1303361View attachment 1303362

Are you still running through this process or was a solution found?

Shooting a Proof pre-fit 6.5, Staball 44.1, 140g pills, Lapua LRP, Fed210....hilarious reading your first post it's literally me. Fire forming has been the only time my shoulders weren't messy(no FL resizing done on virgin brass). After 1st full length poof there ya go. Most accurate rifle I've ever owned and at ELR doesn't make a hill of beans. Checked velo and SD/ES at 2500 rounds and same as after barrel sped up at around 200 rounds.

At this point I just look at it as an annoyance, but would be fun to eventually find out the culprit. Have my next Proof back up ready to go on any day when this one says no mas. So interested to see if it's possibly something just with this barrel and my replacement takes care or it. Either way not inclined to burn too many brain cells or time over it given how well it shoots.

Thanks for your input.