Case Head Separations

[HuntnID]

So I've encountered an issue with my 338 Lapua where I've been getting these case head separations on brass.

The rifle did it to some old brass(case on the left in photo) that I had about 8 firings on so I switched to some newer brass and while it didn't do it to every piece, there is still a mark on the brass and it cracked the brass on 1 of the 3.(cases on the right in photo).

I checked the headspace with go and no-go gauges and it was good.

It was suggested that it could be bolt nose recess is in excess. I checked it as best I could with tape on the bolt nose and as best as I could tell it was about .023" which seems excessive and everything I've found suggested it should be .005".

Do the photos of this brass look consistent with what you guys have seen caused by excessive bolt nose recess?

 

[bigngreen]

Not bolt nose, that's brass stretch. What brand brass?

 

[waspocrew]

How much are you bumping your shoulders back when sizing the cases?

 

[VinceMule]

Measure the headspace length of a fired case, then measure the headspace length of the case after you have sized it. What is the difference?

Web dimensions measured with a micrometer to the 0.0001

new case web dimension
Fully formed case web dimension with easy extraction
Formed case dimension that needs full length sizing, has difficult bolt lift
Sized case dimension exhibiting easy bolt close

Note: range pick up brass has the tendency to "normalize" to a larger dimension AFTER you have sized it, may take 6months or longer for the brass to swell back out or "spring back".

 

[HuntnID]

I've sizes the shoulder back .009". I know a lot of guys only bump .003 but is .009 the difference?

 

[bigngreen]

There's your issue!! Every firing your blowing the case back .009 and that brass stretches at that point. You'll be able to feel the thin spot on all your cases with a pick.

 

[VinceMule]

Huntn, find a case where the bolt closes with some resistance. Then back off the sizing die from it's current setting, and start screwing the die down tiny bits at a time. Each time you size, clean the case, and check to see how the bolt closes. Continue screwing the die down tiny bits at a time, and when the bolt goes from some resistance to easy closing, measure the headspace on that length and record that length.

On occasion, brass may spring back a little where you went from easy bolt closing to slight resistance, and in that case, you want to push the shoulder back a little bit more.

You deal with two dimensions, the dia of the web and the headspace length. Sometimes the dia at the web is the problem and in order to reduce that dia, you have to push the shoulder back more than you like. In this case, you just watch for the bright line around the case, discard that brass when necessary.

Things get a lot more complicated and expensive when you want to get a custom fit to avoid these issues.

 

[Phil Rizzo]

What's the shoulder angle on that case?

 

[MagnumManiac]

I've sizes the shoulder back .009". I know a lot of guys only bump .003 but is .009 the difference?

This is the sole cause of your case head separations.
YOU are causing excessive headspace, stop doing it!

Cheers.
P. S.
The sloping shoulder and case body on the 338 Lapua is another cause of NEEDING to have absolute minimum HEADSPACE, no more than .0015".

 

[HuntnID]

I copy that. I thought .002 was for guys that wanted a tight fit and going a bit over that helped for more reliable chambering. I'm adjusting my dies then.

 

[bigngreen]

It's all good, it's how most of us learned the same lesson.
You'll want to go through your brass and use something to feel inside and cull out any thin brass or just start over fresh.

 

[Horniac]

Huntn, find a case where the bolt closes with some resistance. Then back off the sizing die from it's current setting, and start screwing the die down tiny bits at a time. Each time you size, clean the case, and check to see how the bolt closes. Continue screwing the die down tiny bits at a time, and when the bolt goes from some resistance to easy closing, measure the headspace on that length and record that length.

On occasion, brass may spring back a little where you went from easy bolt closing to slight resistance, and in that case, you want to push the shoulder back a little bit more.

You deal with two dimensions, the dia of the web and the headspace length. Sometimes the dia at the web is the problem and in order to reduce that dia, you have to push the shoulder back more than you like. In this case, you just watch for the bright line around the case, discard that brass when necessary.

Things get a lot more complicated and expensive when you want to get a custom fit to avoid these issues.

Not to high jack this thread but it looks like the OP has the answer to his problem and I am trying to avoid case separation and excessive head space on a potent cartridge.

I am just starting to reload and am trying to bump the shoulders .002 on my once fired 26 Nosler cases using a Lee die set. I am using a 420 comparator to measure to the datum line on the shoulder and my cases have been getting longer not shorter which I know is normal to a point. I keep screwing the die down but it is not doing anything and I am almost out of threads.

I have also put the resized cases in my Fierce Rifle (less firing pin) to check bolt drop like I have seen on YouTube and no luck so it seems to confirm my shoulders aren't getting bumped.

Any suggestions as to what I might be doing wrong? I thought of maybe buying another brand of die but it seems the Lee dies should work.

Thanks for any suggestions/help!

 

[biednick]

Not to high jack this thread but it looks like the OP has the answer to his problem and I am trying to avoid case separation and excessive head space on a potent cartridge.

I am just starting to reload and am trying to bump the shoulders .002 on my once fired 26 Nosler cases using a Lee die set. I am using a 420 comparator to measure to the datum line on the shoulder and my cases have been getting longer not shorter which I know is normal to a point. I keep screwing the die down but it is not doing anything and I am almost out of threads.

I have also put the resized cases in my Fierce Rifle (less firing pin) to check bolt drop like I have seen on YouTube and no luck so it seems to confirm my shoulders aren't getting bumped.

Any suggestions as to what I might be doing wrong? I thought of maybe buying another brand of die but it seems the Lee dies should work.

Thanks for any suggestions/help!

Sometimes virgin brass is so short the first firing doesn't fully form the case to the chamber. It's possible you're trying to push the shoulder back farther than you want to. I typically take about 10 cases and reload them until the action is stiff to close, then measure the shoulder and set my dies to bump back about .002" from there. From that point on I know my die will properly size brass that needs it and not touch new brass that's not yet long enough to need it.

Some guns are too stiff for the bolt to drop like you see on Youtube no matter what you do. Try it with an empty action. If the bolt won't drop closed with an empty action you'll never get it to drop closed on a piece of brass.

I've occasionally had to turn a little bitt off the bottom of a die to properly size brass for real tight chambers. You can grind the shell holder down to achieve the same thing.

 

[Pudgy]

Not to high jack this thread but it looks like the OP has the answer to his problem and I am trying to avoid case separation and excessive head space on a potent cartridge.

I am just starting to reload and am trying to bump the shoulders .002 on my once fired 26 Nosler cases using a Lee die set. I am using a 420 comparator to measure to the datum line on the shoulder and my cases have been getting longer not shorter which I know is normal to a point. I keep screwing the die down but it is not doing anything and I am almost out of threads.

I have also put the resized cases in my Fierce Rifle (less firing pin) to check bolt drop like I have seen on YouTube and no luck so it seems to confirm my shoulders aren't getting bumped.

Any suggestions as to what I might be doing wrong? I thought of maybe buying another brand of die but it seems the Lee dies should work.

Thanks for any suggestions/help!

you will need to remove the firing pin AND the ejector from the bolt - before you can use the drop test.