Strange scoring on case brass

[zambezi]

I have been shooting factory ammunition and also reloading for 6.5PRC. The Hornady Hunter is supremely accurate. But it is lead core, so some copper development is neccessary.

Sorting some reloads for testing I spotted an odd and very shallow scoring near the case head of some once-fired brass . It is definitely 0.001" or less. Barely discernible by fingernail. And it has been imposed on the outside of the case and is not mirrored on the inside. I.e. it is not incipient case-head separation.

That line is not apparent on new cases. On some once-fired cases it covers perhaps 270° of the case radius. On others perhaps 20°. So first up I checked the rifle chamber for burrs or debris . Nil found. Next I checked the Hornady Match Grade sizing die mouth at the appropriate height . Nil imperfections found. Finally I checked the bullet seating die. The design has a circlip retainer for the sliding center core and that does protrude at about the same height I can see the scoring, but does not seem to foul the case in operation. Also, if it was this, surely the scoring would be vertical, not tracking the circumference? Anyway, I trimmed this .


I have some range time this weekend. My plan will be to check cases at every step: (1) on extraction from chamber (2) after resizing (3) after bullet seating.


Any wisdom/experience of this kind of superficial scoring on once-fired brass?

 

[enfieldspares]

Maybe from a red or black plastic "clip" type ten round strip such as Norma and many USA makers pack their ammo in?

 

[Alantoo]

How does it align with your annealing chuck?

Rough edge on the lip of the magazine as you roll it in?

Alan

 

[sh1kar]

microscopic grit in the chamber, working bolt turns the case in chamber as load in?

S

 

[zambezi]

Maybe from a red or black plastic "clip" type ten round strip such as Norma and many USA makers pack their ammo in?

Always worth a check.

The Hornady packaging is loose with no obvious impact to any cases which all appear uniformly perfect . And, for comparison, unfired and once-fired [and sized] side-by-side:

 

[zambezi]

microscopic grit in the chamber, working bolt turns the case in chamber as load in?

S

Possibly, but extensive borescope inspection found none in the chamber. Also, if it were grit, I would suspect the location to vary between cases/chambering iterations. It is always the same height above the case head face.

Range firing clean [factory] ammo will test this theory.

 

[MarinePMI]

It's just the line where the sizing die actually stops sizing the case. Most dies do not size all the way down to the rim (which is impossible, since the case holder covers the rim and part of the base of the case).

Not a big deal, and is seen quite often.

 

[zambezi]

your annealing chuck?

Looking like a front runner now!

Initially I did not think that likely as case fits loosely enough . And the height the case sits in the holder does not correspond to the height of the scoring . But...

...a close inspection of the annealer holder does indeed show some burrs on the lip of its mouth .



Now when I replay how I anneal the brass, I can see when the burr and the site of the scoring might align: (1) insert case in holder and rotate in flame slowly (2) approx 6 secs later, invert cordless drill and drop case into cooling pan. That is the rough sequence, but actually what I usually do to expedite the hot case's release is give the cordless drill a little "rev". I reckon at that point, case part way out already, the burr is probably in line with the mark level I am seeing.


Test on Saturday!

 

[Alantoo]

View attachment 220587View attachment 220586

I initially thought you were referring to the short scratch in your highlight rectangle...made by a part rotation. The later photo shows it evenly marked all-around the case and looks suspiciously like a ridge in the chamber being imprinted on firing....unless you have been spinning the cases in something else prior to or post firing.

Alan

PS Our posts crossed in the ether...so you were referring to the shorter scratch?

The sizing die mark @MarinePMI referred to I thought was the one nearer to the case head, and is more a change of surface texture than a shiny scratch.

 

[zambezi]

It's just the line where the sizing die actually stops sizing the case. Most dies do not size all the way down to the rim (which is impossible, since the case holder covers the rim and part of the base of the case).

I thought same was possible, but then I checked how deep cases rise into sizing die. Scoring appears to be higher still

The sizing die mark @MarinePMI referred to I thought was the one nearer to the case head, and is more a change of surface texture than a shiny scratch.

short scratch in your highlight rectangle...made by a part rotation. The later photo shows it evenly marked all-around the case and looks suspiciously like a ridge in the chamber being imprinted on firing....unless you have been spinning the cases in something else prior to or post firing.

Yup. Read #8 again.

To shake cases free of the annealer holder, I spin them out. Sometimes short spin, sometimes long. So a short scatch on some and a long scratch on others makes sense.

 

[MarinePMI]

Are you storing your ammunition/brass in plastic boxes? I've seen marks before from the cases rubbing against the divider walls. Easy way to test is drop the case in a storage box, and see if it lines up.

 

[zambezi]

Are you storing your ammunition/brass in plastic boxes? I've seen marks before from the cases rubbing against the divider walls. Easy way to test is drop the case in a storage box, and see if it lines up.

That was the check in post #5. The lip of the Hornady packaging sits mid case. No smoking gun there

 

[MarinePMI]

That was the check in post #5. The lip of the Hornady packaging sits mid case. No smoking gun there

Sorry; sitting in a telecon for work, and skimming too much.

 

[zambezi]

OK. Definitive answer: rifle chamber is imposing scoring on case.

Today I fired a bunch of virgin Hornady Hunter factory rounds and whereas they were blemish free prior to insertion in the rifle, they all had faint scoring post extraction. I.e. the image below is immediately post shooting and before cleaning, annealing and re-sizing.

So I need to take a closer look at the chamber and give a [gentle] polish wherever this burr resides.

 

[zambezi]

Finally got around to reviewing the chamber of the 6.5PRC.

I can definitely see scoring that corresponds with shallow marking on cases. It is near the breech in the roof of the chamber [below the scope].

I cannot reach in there with my finger, so cannot ascertain severity, digitally. It is not grit, but may have been caused by grit.

Any remedy suggestions?

 

[MarinePMI]

Looks like the chamber reamer caught a chip, and put a slight gouge in your chamber. It shouldn't really affect the brass or the rifle's ability to shoot well IMHO.

If there is a burr somewhere along that gouge, a slight honing of the chamber should clean that up easily. A q-tip run around the chamber should detect a burr and leave a slight tuft of cotton to identify it.

 

[Alantoo]

On first principles...

If the mark on the case is concave then it is the raised side/levee of the score mark in the chamber that you may be able to push back down with a burnisher.

If the mark on the case is convex/raised then the case is being pushed into a score in the chamber and nothing will really help...polishing it out will only spread the issue further.

It is probably a combination of both raised edge and score...you would reduce the case marking and the size of the score by burnishing the ridge(s) down...

Alan

 

[Ronin]

Solution

If nothing affecting extraction - leave alone

If offending aesthetics - pull barrel and polish chamber

It’s a mark caused during the chambering process that hasn’t been polished or spotted during inspection