Sooted shoulders, any ideas?

[Creedmoor shooter]

I'm not sure this is a problem or not. Rifle shoots fine. But I'm getting some soot around the shoulder of my cases. Never goes past the shoulder. It didn't do it on virgin brass but now it's doing it on sized brass. I've tried no shoulder bump, .002 bump, and longer but no matter what it still does it. 6mm creedmoor running a 109 berger at 3070ish fps. Here's a pic of the shoulders then some groups I shot yesterday. Just curious if anyone has an idea as to why it's doing this all the sudden

 

[Black Hat]

Causes can be, to light of a load no expanding then neck on firing, the brass necks may be getting work hardened (reason why it's not doing it on new brass?), brass is oversized too much headspace.

I would anneal the cases, double check the shoulder bump, and if that doesn't work try and find a different powder, what are you using now, it would be hard to change anything with those groups though!

Or just shoot it, you will eventually end up with carbon in the throat, so make sure you clean the chamber.

 

[Creedmoor shooter]

Causes can be, to light of a load no expanding then neck on firing, the brass necks may be getting work hardened (reason why it's not doing it on new brass?), brass is oversized too much headspace.

I would anneal the cases, double check the shoulder bump, and if that doesn't work try and find a different powder, what are you using now, it would be hard to change anything with those groups though!

Or just shoot it, you will eventually end up with carbon in the throat, so make sure you clean the chamber.

This is once fired lapua brass, h4350, with a cci 450. I'm not really able to change powders. I have about 12lbs of h4350 that I've got to use.

 

[Petey308]

It's definitely not uncommon. Typically a lighter load causes it and/or large clearance in your chamber in relation to the sized cases.

Residue left on the case or chamber can exacerbate the issue and allow more carbon to adhere.

Another thing that causes it is premature bolt release with a gas gun.

Ultimately it's really not a big deal. It'll clean up fine. Just keep your chamber clean so you don't get a carbon ring that will eventually spike your pressures.

You could take a few cases and do a pressure test. Just start at the load you're at there, then load up one each round in .5gr increments and shoot them in order until you get signs of excessive pressure. See if the carbon goes away as the powder charge increases. You'd need to scrub the chamber after each round though so you're not just re-imprinting the carbon from the chamber to the next case. That could at least tell you if it's pressure related.

 

[Creedmoor shooter]

It's definitely not uncommon. Typically a lighter load causes it and/or large clearance in your chamber in relation to the sized cases.

Residue left on the case or chamber can exacerbate the issue and allow more carbon to adhere.

Another thing that causes it is premature bolt release with a gas gun.

Ultimately it's really not a big deal. It'll clean up fine. Just keep your chamber clean so you don't get a carbon ring that will eventually spike your pressures.

You could take a few cases and do a pressure test. Just start at the load you're at there, then load up one each round in .5gr increments and shoot them in order until you get signs of excessive pressure. See if the carbon goes away as the powder charge increases. You'd need to scrub the chamber after each round though so you're not just re-imprinting the carbon from the chamber to the next case. That could at least tell you if it's pressure related.

I've ran the 109s well in excess of 3100 fps and it still does it so id say not a pressure thing

 

[Petey308]

I've ran the 109s well in excess of 3100 fps and it still does it so id say not a pressure thing

Pressure is just one possibility

 

[xsn10s]

It makes me wonder if you're gettting a mild double spike in pressures. I've seen it on 7 RUMS and it can cause dents in the shoulders. Slow powder? Ball powder? What primers? Same load for virgin brass and reloads? If so maybe annealing is needed.

 

[xsn10s]

That's a different, more extreme VLD chamfer. The rounded shoulder makes me think it the pressures are lower. But the velocity and accuracy is good.

 

[xsn10s]

I'd hate to change anything when it shoots like that. To me it looks like the case isn't sealing well on initial ignition. Maybe try more neck tension, a hotter primer, or even a Lee Factory crimp.

 

[.30-06]

low pressure. HS ? Nah. Even fully sized the firing pin pushes the case forward before firing.

 

[Creedmoor shooter]

I'd hate to change anything when it shoots like that. To me it looks like the case isn't sealing well on initial ignition. Maybe try more neck tension, a hotter primer, or even a Lee Factory crimp.

This was my thought at well. I'm running lapua srp brass with a cci 450. It didn't do this with virgin brass at much milder loads so it was just alittle bit of a head scratcher for me. Ive tried not shoulder set back and it still does it. I'm running .003 neck tension and my powder is h4350. I have some lrp brass I can try in it to see if it changes anything

 

[Creedmoor shooter]

I really don't want to run the rifle any hotter than what it is now. This is a new prs rifle I just built so I'd like to keep the pressures alittle lower as prs is already hard on barrels.

 

[Hard rock]

I really don't want to run the rifle any hotter than what it is now. This is a new prs rifle I just built so I'd like to keep the pressures alittle lower as prs is already hard on barrels.

I would say it's a case neck and clearance issue, in the chamber , but no big deal , you probably can tweak it and improve it some but it's not worth the time , load it up and go shoot.

 

[Creedmoor shooter]

I would say it's a case neck and clearance issue, in the chamber , but no big deal , you probably can tweak it and improve it some but it's not worth the time , load it up and go shoot.

That was my thought. It's shooting ok so I'll just keep that chamber/throat clean. I'll probably still tinker with a few things though tonsee if I can figure it out