Not Sure What Caused This

[centershot]

Had a rifle re barreled a few months ago and I get this soot deposite on the cases. Never had this happen to this degree before. I backed off the reloading sizer a full turn so there was plenty of positive head space. Did not help. Am using Nosler brass and it seems to be thinner than the Winchester. Loaded Nosler cartridge measures 0.28275 ". Fired is 0.28175". Nosler brass measures 0.0135" in the neck wall thickness. Winchester measures 0.0145". The reamer print says 0.2580". Do not think the Winchester brass does this soot thing.
I think the chambering job is okay. Within .0005". Loaded round is .0075" less than fired case. Does not seem excessive. Does this with all powders tried.
Question is, am I just being over the top with this? Cartridge is .257 Ackley.

 

[Nowhere Man]

New brass or brass previously shot in the old barrel? If old brass, try some new stuff and see if the problem disappears.

 

[RegionRat]

Check your inspection numbers.

... "Loaded Nosler cartridge measures 0.2185 "...

0.28175" - 0.2185" = 0.06325" This sounds wrong.

0.28175" - 0.2580" = 0.02375" This also doesn't make sense since your reamer print value of 0.2580 is only a mil over the bullet diameter?

0.257" + 2x(0.0145") = 0.286"
0.257" + 2x(0.0135") = 0.284"

I'm guessing your neck would be in the range of 0.287 to 0.291 or thereabouts.

The main point is to give the brass a chance to get normalized to the chamber and your dies. If it doesn't clear up or they don't perform well, then you would want to revisit with an inspection of the chamber.

 

[centershot]

Brass has been fired several times.

 

[RegionRat]

Brass has been fired several times.

Sorry, more questions than answers...

In just this chamber?

Annealed or no?

Have you taken a look with a borescope?

 

[Webster]

Had a rifle re barreled a few months ago and I get this soot deposite on the cases. Never had this happen to this degree before. I backed off the reloading sizer a full turn so there was plenty of positive head space. Did not help. Am using Nosler brass and it seems to be thinner than the Winchester. Loaded Nosler cartridge measures 0.28275 ". Fired is 0.28175". Nosler brass measures 0.0135" in the neck wall thickness. Winchester measures 0.0145". The reamer print says 0.2580". Do not think the Winchester brass does this soot thing.
I think the chambering job is okay. Within .0005". Loaded round is .0075" less than fired case. Does not seem excessive. Does this with all powders tried.
Question is, am I just being over the top with this? Cartridge is .257 Ackley.

I you checked shoulder set back with a bump gauge?

 

[FeMan]

Looks like the result of old brass in a new chamber. Id try new brass and see if that doesn't solve it.

 

[centershot]

New brass is the same.

 

[centershot]

Yes. This chamber. No bore scope. Do not know what a bump gauge is. One rifle.

 

[joshb]

I can’t make sense of your numbers, either.
“Loaded Nosler cartridge measures 0.28275 ". Fired is 0.28175".”????????
“Loaded round is .0075" less than fired” ?????

 

[RegionRat]

A bump gage is short for shoulder bump gage, also called a headspace comparator.

It is used to measure how much you are sizing down the shoulder.

It is generally a precision hole diameter made at the shoulder datum diameter on the cartridge design print. The tool can be clamped onto a 6" caliper and zeroed to a fired case and then used to observe sizing die adjustments.

I don't think the 257 AI was SAAMI adopted, so the shoulder datum diameter and length can be a little arbitrary depending on who makes the reamer.

Here is a typical Hornady shoulder bump gage tool for reference.

https://www.hornady.com/headspace-bushings#!/

In your position, I would start a conversation with the gunsmith who chambered your bbl and ask him for advice and a copy of the reamer print. That way you have it from the horse's mouth as well as the prints used for the reamer. Sometimes the actual reamer and the print can be slightly different. A chamber casting will generally answer how the actual chamber ended up.

 

[M-61]

I can’t make sense of your numbers, either.
“Loaded Nosler cartridge measures 0.28275 ". Fired is 0.28175".”????????
“Loaded round is .0075" less than fired” ?????

Yes. Recheck your numbers or your sentence structure. Or just pause to think how it could be smaller after firing. I'm betting on a typo.
Then again maybe I'm reading it wrong.

 

[243winxb]

Throat/free bore length to long? Try, faster burn rate powder, mag primer, more neck tension, shorter COL. Heavier bullets.

Any thing that will increase pressure may help?

Your soot not bad enough to worry about it. Here is bad-

 

[tonyb]

Throat/free bore length to long? Try, faster burn rate powder, mag primer, more neck tension, shorter COL. Heavier bullets.

Any thing that will increase pressure may help?

Your soot not bad enough to worry about it. Here is bad- View attachment 1288862

That’s the result of a hand load that is way under loaded, seen it several times…

 

[Lefty Trigger]

Running a silencer? Those cause some backpressure that could lead to this.
I personally think it's a headspace issue, necks look good but shoulder dirty. Need to make sure your not pushing the shoulder back too far with your resizing die.

 

[JFrank]

Running a silencer? Those cause some backpressure that could lead to this.
I personally think it's a headspace issue, necks look good but shoulder dirty. Need to make sure your not pushing the shoulder back too far with your resizing die.

Headspace is a definite probability. Along with light load

 

[centershot]

Remeasured. Loaded is .2815. Fired is .2875. As I said in the first post, I backed off the sizing die one full turn. Do not think it is a head space problem. This was not a light load. I will have to fire the Winchester brass to see if this is different.

 

[joshb]

What was the shoulder measurement of your fired case?
Does a fired case chamber without resistance?
How far are you pushing the shoulder back? Should be only 2 thousandths!
Sometimes you have to fire a case twice to get it to form to your chamber.
Then you bump it back 2 k.

 

[LCazador]

Brass has been fired several times.

Your measurements are skewed. It's not the brass, maybe your die set up.

 

[dellet]

I hate to say it again, but check your numbers at the neck, in a couple places.

The neck thickness you listed, .0135"-.0145" + bullet diameter don't match up to loaded diameter.

Maybe your measuring a big doughnut in the neck, maybe a bullet diameter issue, maybe something really strange like crushing the bullet instead of expanding the case when seating.

If some how the bullet is undersized, it won't seal the bore and you won't have the pressure you would normally expect.

It might be worth seating/then pulling a bullet and checking diameter both before and after..