I seriously doubt this is case head separation but what do you guys think?

[timberelk]

Are the cases you show in the picture just fired and not resized yet, or are the pictures of what they look like AFTER removing them from the sizing die? If they are fresh from the chamber after firing, I would think it is possibly from the chamber being rough. It doesn't appear to be case head separation.

The picture is brass that was fired and only fired, not resized or cleaned.

Looks like I posted at the same time as you did, please read post #14 if you get a chance.

Everyone's help on this is appreciated! I would really like to avoid damage to me or my gun from a case separation

 

[Laelkhunter]

Follow previous advice about bumping the shoulder. I would definitely tumble the brass before running through your sizer. If you don't, you will end up with crap getting into the sizer walls, and then you will get scratches on the cases every time you resize them.

 

[Barrelnut]

All my cases from last time I shot have these distinct part were everything above the line is shinny/reflective brass while everything below the line is dull. Maybe the dull portion of the case is the part that expanded?

These loads were intro loads and this was the second time the brass has been fired. Primers look great and bolt lifted very easy after firing.

Green arrow is pointing to the dividing point between shinny and dull brass.

Cases were clean and shot in my chamber and then were put right back into the box. Did not touch the ground or any dirt.

That is normal for all resized brass. Put your calipers right at that ring line and measure. Next put your calipers right at bottom of the dull area. You will probably find a .002 difference. All of this happens because the dull section at the very bottom is the thick part of the brass called the web. It doesn't expand like the rest of the sides of the case and the dies never touch it when you run the brass thru the die. If you ever start to see a very thin shiny ring about .100 up from the current line you are talking about, that will be a case separation starting.

Look like those are 308 cases? that type case has a shallow 20% shoulder angle angle. This allows the brass to flow a lot toward the neck when you FL size the case. The the expander ball can pull the neck longer too when the expander exits the neck and exasperate things. This is probably why the overall length is growing 005-.010 each time. Bumping the shoulder back too far causes more of this too. Just try to bump the shoulder back about .002

 

[timberelk]

Correction to post #14. The factory loads that I fired stretched to 2.028-2.030 so they are stretching from .003-.005" where my reloads are stretching .005-.010

 

[timberelk]

That is normal for all resized brass. Put your calipers right at that ring line and measure. Next put your calipers right at bottom of the dull area. You will probably find a .002 difference. All of this happens because the dull section at the very bottom is the thick part of the brass called the web. It doesn't expand like the rest of the sides of the case and the dies never touch it when you run the brass thru the die. If you ever start to see a very thin shiny ring about .100 up from the current line you are talking about, that will be a case separation starting.

Look like those are 308 cases? that type case has a shallow 20% shoulder angle angle. This allows the brass to flow a lot toward the neck when you FL size the case. The the expander ball can pull the neck longer too when the expander exits the neck and exasperate things. This is probably why the overall length is growing 005-.010 each time. Bumping the shoulder back too far causes more of this too. Just try to bump the shoulder back about .002

You sir are correct. Tested 4 different fired reloads and I'm seeing .0015-.002" difference between where it is shinny and where it is dull.

You are also correct about the carriage. It is a 7mm08 so essentially a 308 Case.

Right now I'm setting the should back about .004. I can try to set the shoulder back only .002 but will that stop my overall brass length from growing .005-.010?

 

[L.Sherm]

It is quite possible your comparator is not measuring right on the datum line of your shoulders. If you ever have a gun built have your smith make one with the reamer used I do mine and customers who want one out of a piece of the barrel it can also be used to find the lands in a new barrel

 

[L.Sherm]

Try .001 to no more than .002 and see the difference it will tell you then.

 

[Barrelnut]

Right now I'm setting the should back about .004. I can try to set the shoulder back only .002 but will that stop my overall brass length from growing .005-.010?

It will help. How much so is hard to say for sure. Lots of variables. Even depends on how hard the brass is. Cartridges that have sharper shoulders seem to grow less.

That .010 growth you are seeing, and ends up getting trimmed off when the necks are trimmed, has to come from somewhere... It tends to come from that web junction area where the brass goes from thick to thin. That why the brass gradually gets thinner there.

Having a smooth, lubed expander call can help too.

 

[J E Custom]

There is only one way to tell if the case is thinning in this area and may separate later, sacrifice one case and section it , then Mic the thickness up and down the body and look for thinning in this area. (It should get thicker the closer to the web you get). if it is close to separation you will be able to see it on the inside.

One case is nothing, compared to losing all of them and having to fish the cases out of the chamber. If it is stretching, do a minimum sizing to make it last longer and at the first sign of failure, through all of them away before they damage your chamber.

J E CUSTOM

 

[timberelk]

There is only one way to tell if the case is thinning in this area and may separate later, sacrifice one case and section it , then Mic the thickness up and down the body and look for thinning in this area. (It should get thicker the closer to the web you get). if it is close to separation you will be able to see it on the inside.

One case is nothing, compared to losing all of them and having to fish the cases out of the chamber. If it is stretching, do a minimum sizing to make it last longer and at the first sign of failure, through all of them away before they damage your chamber.

J E CUSTOM

I'm going to cut one open tomorrow after work and take a look at it!

So you're saying trim the brass to the max overall brass length (2.035") instead of trimming to 2.025" so the brass can't exoand any further?

 

[Pdvdh]

I look down into the case with a flashlight. If case head stretch / separation is progressing, I find it easy to see looking down the 7mm and .308 case necks. There will be a donut shadow/ring. Shadow ring is caused by the light being unable to shine into the recess of the circular ring of thinner brass where the sidewall is separating.

 

[timberelk]

I look down into the case with a flashlight. If case head stretch / separation is progressing, I find it easy to see looking down the 7mm and .308 case necks. There will be a donut shadow/ring. Shadow ring is caused by the light being unable to shine into the recess of the circular ring of thinner brass where the sidewall is separating.

I just tried this on a few random cases and couldn't see anything abnormal (no shinny ring or indent) but the inside of the case is coated with the powder residue so it all just looks light black inside the case

 

[bigedp51]

Chambers and dies vary in size, your chamber diameter can be on the plus side and your die could be on the minus side of SAAMI dimensions.
When you full length resize a case the brass has only one direction to move, and that is upward in the die. Meaning the more you squeeze a fired case the longer the neck will become.

Look at the exaggerated illustration below and how sizing (squeezing) the case makes it grow. And when sizing the case shoulder is also moved forward. Example if you put a .010 feeler gauge between the bottom of the die and the shell holder you could make the case longer in headspace than the chamber. Meaning you might not be able to close the bolt because the case shoulder location was squeezed forward.

Below look at the blue, red and green dotted lines, in real life you want the shoulder .001 to .002 below the red dotted line.

I collect older milsurp rifles with larger diameter chambers and the cases will expand more when fired. And when full length resized they will grow in length more than in a smaller diameter chamber.

And the marks on your cases above the base is where the case expanded and contacted the chamber walls.

 

[timberelk]

I also noticed a small intent in 5 if the 20 cases. Not sure where these intent came from. They weren't like this when I loaded them up