Raised Ring at Base of .223 case?

[WindSurgeon]

This is a new one for me so looking for some opinions as to the cause and meaning. I have seen the thin ring at the bottom of cases as they reach the end of their life and always take that as a sign of a potential case separation about to happen so I cull the cases. If you look at the photo, you can see that the ring is raised. When I feel the inside of the case with a bent paper clip and look at the inside under magnification, there is no thinning signs present at the location of the raised ring. Also, there are no signs of crazing or cracking.

-Lapua brass
-fired 6 times. 25% of that batch of cases (86 cases) had this, the others looked fine
-23.9 grains Varget under 77 gain burger bullets, .001" off the lands (stony point tool)
-Fired from an AR15 mil spec chamber
-Full length resized with RCBS die after each firing

What is it? What's the cause? What's the solution?

I am not using these, but want to prevent it in the future.

 

[Eddie Harren]

I believe that that potion of your case is solid. It appears that you may have a chamber, on the large side, and a die on the small side, of acceptable tolerances. Cut a case in half lengthwise and see what part of the case is solid.

 

[BoydAllen]

+1

 

[expiper]

whoever chambered that bbl. did not round off (champher) the chamber,,,,that happens to most cases but is not obvious becasue it is not a sharp edge like you have,,,Roger
PS...I am a fan of Lapua cases,,,BUT not in a rattle gun,,,,the chambers are usually "loose" compared to a bolt gun,,,,and the LC brass is made to shoot in an auto/semi auto military weapon ,,,the case head is much thicker/taller/further up the ctg case to prevent this from happening because of the big chunk of metal in that area,,,that is why most LC brass has less case capacity,,,not because the walls are thicker only,,but becasue of a thicker case webb,,,,

 

[WindSurgeon]

Would a die change help? The RCBS is about as basic as it gets. The die is a standard FL, perhaps a small base die would be better?

Strange that it showed up on these, but not my other brass. I have shot LC in the past without this issue.

 

[BoydAllen]

Just out of curiosity, measure the diameter of a new Lapua case at the top of the extractor groove and then measure the same area of the case pictured. Let us know what you find. A small base die would be going in the wrong direction. Has the Lapua brass given better accuracy in your AR?

 

[spclark]

What brand of AR / 'milspec' chamber? Does new, nothing-done-to-it brass chamber and shoot OK? How does the base-to-shoulder dimension of new brass compare to once-fired?

To my eye it looks like your chamber might be a little short, leaving an unsupported case head area at the breech that then gets swaged to a larger diameter with each firing.

Your headspace may be OK while the breech end of the barrel is a little short or faced back too steeply. Mil-spec is generous compared to a match reamer profile but all that's in front of the condition forming that ring. Small base die might help if used repeatedly but it's not a solution as much as it is a band-aid.

Brass moved under pressure, that's a fact. Case heads are pretty thick just in front of the extractor groove. Head separation typically happens a little farther forward of where the case walls begin, anywhere from 1-2mm / 1/16" up to about 12mm / 1/2".

What kind of loads do you typically use? Lapua's noted for case capacity on the low side but comparable to Lake City brass used by many competition service rifle shooters. Using match rifle loads in a mil-spec chamber is gonna move your brass more than you need to for long case life.

 

[stool]

if the brass is not fully in the shell holder, it can tilt the case , and pinch some brass at the base....just like that..
a pc of media in the extractor groove or dirt on the underside of the shell holder..

 

[243winxb]

The web expanded a little more on each firing. After 6 loadings its time for new brass. Reduce powder charge for longer case life.

 

[BoydAllen]

Another thing, if you are using the same load in LC and Lapua, and the Lapua cases are heavier, and therefore have less capacity, you will be generating more pressure.

 

[spclark]

Another thing, if you are using the same load in LC and Lapua, and the Lapua cases are heavier, and therefore have less capacity, you will be generating more pressure.

In some capacity testing I did a few years ago I found Lapua's 223REM brass to be just a bit heavier than the various years of LC I had on hand. In water capacity, about half a grain less. Compared to WIN or R/P those two are more like 1-1/2 to 2+ grains less in volume.

So it does pay to abide by case brand used when taking loads from other sources.

Still, that picture shows a distinct ring embossed very close to the case head. 223 brass can withstand 62,000 psi while design factors with the AR were targeted at 52,000 psi so it's easy to overpower with hand loads and not see evidence of pressure on fired cases until you're well past safe practices.

 

[stool]

do not mix apples and oranges....your comments on 62000 and 52000 are TWO DIFFERENT STANDARDS MEASURED AT TWO DIFFERENT PLACES...
there is little real world difference in the two.....

the throats are diff is the biggest issue.

Another thing, if you are using the same load in LC and Lapua, and the Lapua cases are heavier, and therefore have less capacity, you will be generating more pressure.

In some capacity testing I did a few years ago I found Lapua's 223REM brass to be just a bit heavier than the various years of LC I had on hand. In water capacity, about half a grain less. Compared to WIN or R/P those two are more like 1-1/2 to 2+ grains less in volume.

So it does pay to abide by case brand used when taking loads from other sources.

Still, that picture shows a distinct ring embossed very close to the case head. 223 brass can withstand 62,000 psi while design factors with the AR were targeted at 52,000 psi so it's easy to overpower with hand loads and not see evidence of pressure on fired cases until you're well past safe practices.

 

[WindSurgeon]

Thanks for all the great thoughts. So to some of the questions you all asked, I took some measurements and created this slide of dimensions along with the spec from this site. It does not look all that out of spec, but a thou here and a thou there can add up. The ridge adds to the profile.

I went to Lapua and it provided great .25"-.50" MOA groups so I stuck with it. My experience is that LC proved less consistent and I was trying to keep everything I could as consistent as possible for F-Class shooting at 300 yards. I still use the LC for varmint loads. After finding my accuracy node at 23.9 grains of Varget in the Lapua brass with no pressure signs, I stayed with that and have been shooting it for the last two years. It is coincidentally the listed max load in the Sierra manual for Varget which is AR specific.

I am starting to think that my brass is flowing towards the base if that's possible, or my dies are pushing the brass walls toward the base and creating this ridge as it bunches up above the shell holder (I just looked at the shell holder and it was clean).

 

[WindSurgeon]

photo of brass in shell holder.

Also, the rifle cycles great when I am shooting it with standard, nothing done to it, brass per the question above from spclark.

 

[243winxb]

When you look at the mouth of the die, do you see a bevel? Check the case & chamber drawings here. http://www.saami.org/specifications_and_information/index.cfm?page=CC

RCBS FL dies from 2010 & 1979

 

[stool]

if this ring goes all the way around it is most likey your dies( as the guy above is pointing out).
part way around is a cocked approach into the die.
at the point we see teh ring it is not the chamber that is directly causing the ring as it is outside the chamber of an ar.
someone else pointed out the chamber may be the issue..if it is a bit too large, then the die is working hard .
it is possible the oversized brass is just too much for the die..the lip of the mouth of the die is creating the ring...

would be nice to know the dia and runout of the back of your chamber...

 

[WindSurgeon]

Here is my die:

 

[bigedp51]

Are you using a standard green box RCBS .223 die or the black box AR series dies that are small base?

 

[243winxb]

Posted by Stool

it is possible the oversized brass is just too much for the die..the lip of the mouth of the die is creating the ring...

This would seem to be correct. To know, take measurements on the web area where the ring appears, before sizing . I am guessing its larger than .3789" the maximum SAAMI chamber diameter. If its not to large, try different lube if your using wax. RCBS CASE LUBE-2 may make a difference.

 

[spclark]

Here is my die:

In your photo there's what appears to be something just below (above, when in a press) the radiused mouth that could be the source of that ridge on your brass.

There's a highlight in the pic at that point; is there an edge in your die that's the problem? Even if hard to see you ought to be able to feel it with a straightened paper clip or similar.