Sooted shoulders, any ideas?

[xsn10s]

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

With that powder and primer selection I wouldn't think it's a double spike in pressures or poor ignition. Summer time so the temps should be fine. Did the virgin brass have that chamfer and debur?

 

[Creedmoor shooter]

With that powder and primer selection I wouldn't think it's a double spike in pressures or poor ignition. Summer time so the temps should be fine. Did the virgin brass have that chamfer and debur?

It did. No change other than resizing

 

[Texas Speed Bump]

That happens to me on every round through my Bergara 6.5CM and it happens to other folks I know shooting the 6.5 Creedmoor. It doesn't seem to affect accuracy (I just shot my best 3-shot group yesterday of 0.28" using StaBall 6.5) but have had it happen with factory loads, reloads, and different powders. I just polish the neck with a piece of steel wool for a few seconds when it comes out of the tumbler and it looks like new again.

 

[Hugnot]

I had black stuff deposited on shoulders of .204 R cases. Soot was also deposited on bolt face. Looking at the problem showed the cases needed to be trimmed. Apparently, jamming the mouth of the case against the front end of the chamber prevented complete neck expansion. Trimming the cases fixed the soot situation.

More likely, as mentioned, sounds like neck work hardening. Inadequate seal between neck & chamber, bullet kicked into throat without adequate neck tension caused by work hardening (brass spring back) followed by backed up gas/crud deposition on shoulder. - "It didn't do this with virgin brass at much milder loads". With velocites in excess of 3,000 with 109's sounds like pressures are close to max, like 60K plus. New brass (wirgin brass) would be shorter than multi-fired brass. Possibly brass length to chamber might be worth checking. Annealing makes for nice soft clingy brass (large crystal size) needed for consistent neck tension.

I should be so fortunate to have: "I have about 12lbs of h4350 that I've got to use."

I shoot real cheap, once fired Federal 6.5 CM brass necked down to 6mm CM, turned to .268 with 42.0 gr. AA4350 & Barnes 105 Match Burners & CCI 41 primers. Cases turned to 1.91. Soot & crud now appearing on shoulders so I will anneal & trim to 1.91. Best accuracy sort of (but not quite) approaches that of OP, 3 bullets in same hole. Neck tension approx same as OP's.

 

[VICTORNTN]

Neck sooting is usually caused by the case not swelling enough to seal against the chamber. Sooting going back against the shoulder is sometimes sizing the shoulder back too far.

 

[.30-06]

Neck sooting alone is too much clearance around the neck of the case. IE .30-06 chamber neck is SAMMI .3397 and seated bullet is .332 outside neck diameter.

 

[Creedmoor shooter]

The neck of my brass expands .006 after firing.

 

[Csbc4fun]

That's some great shooting! I'd live with the soot and take those groups.
What brand and type of barrel?
What action?

 

[.30-06]

The neck of my brass expands .006 after firing.

and you don't have soot on the neck, correct?

 

[Creedmoor shooter]

That's some great shooting! I'd live with the soot and take those groups.
What brand and type of barrel?
What action?

It's a pierce engineering action, criterion prefit barrel from NSS with the 183 freebore. Dropped into a MPA matrix chassis

 

[Creedmoor shooter]

and you don't have soot on the neck, correct?

Correct. Mainly just the shoulder

 

[.30-06]

Correct. Mainly just the shoulder

it does happen that way for me on the neck only but not that often on the shoulder, rarely unless it is a low charge. Depends on the powder and load.

 

[jsthntn247]

The neck of my brass expands .006 after firing.

That's one of your problems. Also, try the handle drop method explained by Alex Wheeler when setting your shoulder bump. Some gauges and chambers can be way off and .oo1 on the gauge could be allot more in the chamber.

 

[.30-06]

The neck of my brass expands .006 after firing.

and has to be sized back down to seat bullets. You still get blow by until it expands to chamber dimensions.