Avoiding case head separation by measurement

[Namekagon]

This is a pretty technical brass question for the reloading wizards here.

I have the RCBS case master gauging tool. As my Norma 6XC brass gets up in firings, I use it to check the wall thickness of the case to monitor for impending case head separation issues. Basically the tool allows you to drag a dial indicator along the case the long way measuring wall thickness from the head all the way to the shoulder. As you slide the dial, you can see the brass wall thickness taper from thick at the head to thin at the shoulder.

Thin spots just above the head are detected when the dial needle either pauses or moves backwards as you pull the case. RCBS says if you see this, reject the case. I’m confidant that’s being too conservative for this brass/cartridge, as I’ve noticed some thin spots on cases with only like 5 firings and I know the case is good for more, as I kept shooting them.

I have been using the criteria of any thin spot 0.004” or deeper for rejection. I check each case twice, once each on opposite sides. Using this method, I find I’m rejecting cases about the 10th or 11th firing. That seems closer to reasonable, but the cases still do not show any external signs of separation.

For perspective, I’m measuring a thinning of 0.004” at a spot in the case that would be about 0.032” thick were it not thinned. Some of that may be carbon, as I haven’t tumbled in awhile. So about 13% thinner. Based on this data, do you think 0.004” is a good criteria? Or still too conservative? Thanks!

 

[918v]

I go by shiny ring marks and case growth. Once a case develops a shiny ring in the case head area I know it might let go at the next firing. Usually this happens after the case grows more than .070” . This is fairly predictable.

.004” is nothing. The case will thin by more than half when it separates. Keep shooting them until you see a thin ring.

 

[Namekagon]

I go by shiny ring marks and case growth. Once a case develops a shiny ring in the case head area I know it might let go at the next firing. Usually this happens after the case grows more than .070” . This is fairly predictable.

.004” is nothing. The case will thin by more than half when it separates. Keep shooting them until you see a thin ring.

Do you have a picture of what that ring looks like on a case you’d reject? I can see very faint shiny ring on my cases in that location even after 3 firings when thinning is not detectable. I presume it gets a lot worse, just wondering what to look for. Thanks

 

[GreenGO Juan]

You can look inside the case with a flash light and see the ring forming before its noticeable on the outside, at least in my experience with .308.

Case pre cut-

Cut case because I couldn’t get the camera to pick up the ring.

In the case above the black line is the shadow formed from stretching. This case has well over 10 firings.

No visible ring on the outside.

Measuring sounds like a good idea but a light can do the same.

Made this part of my inspection process.

 

[918v]

Do you have a picture of what that ring looks like on a case you’d reject? I can see very faint shiny ring on my cases in that location even after 3 firings when thinning is not detectable. I presume it gets a lot worse, just wondering what to look for. Thanks

I don’t and the last time I tried to photograph one it was not visible in the picture.

The faint shiny ring is the brass stretching. But the ring I’m talking about is not faint. You will know it when you see it. It will be pronounced and not just cosmetic. You’ll see a physical structural visible groove. At that point the brass has maybe one more firing in it provided you bump the shoulder minimally.

 

[straightshooter1]

Do you have a picture of what that ring looks like on a case you’d reject? I can see very faint shiny ring on my cases in that location even after 3 firings when thinning is not detectable. I presume it gets a lot worse, just wondering what to look for. Thanks

When faint, they still have some life in them. When I see a faint rings (one not associated with what the sizing die leaves), I'll run a bent paperclip over the inside surface and if I can easily feel the depression where the separation has begun, it's time to trash it.

Below is an example of the separation line on the outside that's very distinct. That line starts out fainter than that and though it's faint, it can be seen easily enough. It's better to use a tool like a bent paperclip to reach in and feel the inside rather than depend on what you see on the outside.

 

[Supersubes]

This is a pretty technical brass question for the reloading wizards here.

I have the RCBS case master gauging tool. As my Norma 6XC brass gets up in firings, I use it to check the wall thickness of the case to monitor for impending case head separation issues. Basically the tool allows you to drag a dial indicator along the case the long way measuring wall thickness from the head all the way to the shoulder. As you slide the dial, you can see the brass wall thickness taper from thick at the head to thin at the shoulder.

Thin spots just above the head are detected when the dial needle either pauses or moves backwards as you pull the case. RCBS says if you see this, reject the case. I’m confidant that’s being too conservative for this brass/cartridge, as I’ve noticed some thin spots on cases with only like 5 firings and I know the case is good for more, as I kept shooting them.

I have been using the criteria of any thin spot 0.004” or deeper for rejection. I check each case twice, once each on opposite sides. Using this method, I find I’m rejecting cases about the 10th or 11th firing. That seems closer to reasonable, but the cases still do not show any external signs of separation.

For perspective, I’m measuring a thinning of 0.004” at a spot in the case that would be about 0.032” thick were it not thinned. Some of that may be carbon, as I haven’t tumbled in awhile. So about 13% thinner. Based on this data, do you think 0.004” is a good criteria? Or still too conservative? Thanks!

You didn't say what your sizing process is. For the XC, which is a match chambering with minimal diameter clearances, you should not be separating case heads. It has nothing to do with pressure, and everything to do with how much you’re bumping the shoulders each time. With minimal sizing and occasional annealing, those case should last for dozens and dozens of firings.

 

[GIXXER2000]

I had a chance to talk with the Peterson's Brass design engineer at Shot Show about case head separation. I was have an issues with my 375ct brass after 4 firings. He told me to not bump the shoulder until the case gets hard to chamber. His though was the sizing was over working the brass. I do anneal every firing. So on my next 100 pieces of brass I had a 0 bump until the 4th firing them I bumped .002 and I am now on my sixth firing without any case head issues and the brass chambers like new.. I am not babying my brass either I am running 131.5 gr of N570 pushing a 400 gr CC.

 

[Barelstroker]

This is a pretty technical brass question for the reloading wizards here.

I have the RCBS case master gauging tool. As my Norma 6XC brass gets up in firings, I use it to check the wall thickness of the case to monitor for impending case head separation issues. Basically the tool allows you to drag a dial indicator along the case the long way measuring wall thickness from the head all the way to the shoulder. As you slide the dial, you can see the brass wall thickness taper from thick at the head to thin at the shoulder.

Thin spots just above the head are detected when the dial needle either pauses or moves backwards as you pull the case. RCBS says if you see this, reject the case. I’m confidant that’s being too conservative for this brass/cartridge, as I’ve noticed some thin spots on cases with only like 5 firings and I know the case is good for more, as I kept shooting them.

I have been using the criteria of any thin spot 0.004” or deeper for rejection. I check each case twice, once each on opposite sides. Using this method, I find I’m rejecting cases about the 10th or 11th firing. That seems closer to reasonable, but the cases still do not show any external signs of separation.

For perspective, I’m measuring a thinning of 0.004” at a spot in the case that would be about 0.032” thick were it not thinned. Some of that may be carbon, as I haven’t tumbled in awhile. So about 13% thinner. Based on this data, do you think 0.004” is a good criteria? Or still too conservative? Thanks!

I've never measured the thickness at the area just above the web where the cases thin out but, as soon as I can notice an indent on the inside as shown in GreenGO Juan very nice pic, I just trash em & move on.
I don't think it's wise or necessary to trying to work out the exact thickness before CHS & I'm confident in stating that it's really not worth the risk.
Although you can see down into the case with a torch, I've used a specially fashioned piece of wire for 30 years which I use to feel the case down at the web. If I can feel the pronounced indent I trash em & don't look back.
I think the tool you're using although well made & intentioned, has got you thinking there's a specific thickness that the case web can be taken to.
I've never heard or read of any specific thickness regarding this issue or anyone who has done any testing in this regard so, to answer your question regarding a specific thickness, I'm not aware of such.

 

[Namekagon]

You can look inside the case with a flash light and see the ring forming before its noticeable on the outside, at least in my experience with .308.

Case pre cut-View attachment 7953714

Cut case because I couldn’t get the camera to pick up the ring. View attachment 7953716

In the case above the black line is the shadow formed from stretching. This case has well over 10 firings.

View attachment 7953717
No visible ring on the outside.

Measuring sounds like a good idea but a light can do the same.

Made this part of my inspiration process.

Thanks. It makes sense that a light would work, but when I tried it I could not see much. It might be due to the smaller 6mm neck. If Icut a case I would expect to see exactly what you describe.

 

[Namekagon]

When faint, they still have some life in them. When I see a faint rings (one not associated with what the sizing die leaves), I'll run a bent paperclip over the inside surface and if I can easily feel the depression where the separation has begun, it's time to trash it.

Below is an example of the separation line on the outside that's very distinct. That line starts out fainter than that and though it's faint, it can be seen easily enough. It's better to use a tool like a bent paperclip to reach in and feel the inside rather than depend on what you see on the outside.

View attachment 7953837 View attachment 7953838

Those distinct lines in your photos are exactly what I think I needed to see. Because that is not what I have, so I must only be seeing the faint stretching that @918v mentioned.

As far as using a paper clip, the RCBS tool I mentioned earlier is basically doing the same thing, but measuring it vs feel. The question then became, what measurement is bad?

 

[Namekagon]

You didn't say what your sizing process is. For the XC, which is a match chambering with minimal diameter clearances, you should not be separating case heads. It has nothing to do with pressure, and everything to do with how much you’re bumping the shoulders each time. With minimal sizing and occasional annealing, those case should last for dozens and dozens of firings.

I’m using Forster full length dies and bumping the shoulders .002”-.003”. I know I could get away .001”, but most of my shooting is hunting and the occasional match. I wanted the extra reliability.

I haven’t had any separations after 11 rounds on my oldest brass. Not sure how many rounds is normal, but based on your comment apparently more than I thought! Sounds like they have some life left in them if I anneal them again.

 

[straightshooter1]

Those distinct lines in your photos are exactly what I think I needed to see. Because that is not what I have, so I must only be seeing the faint stretching that @918v mentioned.

As far as using a paper clip, the RCBS tool I mentioned earlier is basically doing the same thing, but measuring it vs feel. The question then became, what measurement is bad?

It's not uncommon to mistake the line that sizing dies leave vs the actual faint head separation line. They can look very much the same.

When using your RCBS Case Master to detect cases head separation, you won't be taking measurements as the measurements can vary from case to case and from one side of the case to the other due to variances in the thickness of the brass. But, running it back and forth (just as I do with my paperclip) you can feel a dip where the separation is beginning. If the tool slides back and forth smoothly over that area where you just can feel anything, then you're good to go.

 

[iceng]

Fully clean your brass. Wet tumbling and get the inside ready for inspection. Do your gauge thing, and use a bore scope, like a teslong, and have a good look.

Ive pushed norma past 20 firings, then the primer pockets were so loose they wouldnt even hold a primer.. 243ai.

 

[RegionRat]

If you minimize the bump, like on the order of 0.002" as discussed above, your case stretch should be steady and easy to judge to stay out of trouble.

A borescope can work, but at some point you will want to cut samples open to learn the process of when to retire cases.

With the case cut open in front of you, the measurements and observations you make with the paper clip or your tool will be less mysterious.

Your 0.004" reading observation may or may not mean anything, but you will know one way or the other once you cut them open. If it is a ring that goes all the way around, it matters.

 

[Yondering]

Thanks. It makes sense that a light would work, but when I tried it I could not see much. It might be due to the smaller 6mm neck. If Icut a case I would expect to see exactly what you describe.

You can't see much because you're trashing brass that doesn't need to be trashed. If there's actually a ring, you'll be able to see it easily through a 6mm neck. I do this even with little 20 Tactical brass, 223 Rem, etc, and plenty of 6mm Grendel. Use a small and bright modern LED flashlight though, not some large old fashioned Maglight or worse - besides not being as bright, the large head does get in the way and makes it a lot harder to see into a case with a small neck.

Looking in the case with a light is FAR more reliable than feeling around with a paperclip, and if you can't see a shadow ring, the brass is fine.

It's also a lot faster than trying to take measurements, and also more reliable unless you're measuring in at least 3 places around the brass. When you do start to get impending separations, you'll see it start often just on one side of the brass and that can be easily missed by measuring in only one place, or even at two points 180° apart if you're unlucky.

I have the same RCBS tool, and IMO you're wasting time and making the process harder than it needs to be by using it for this purpose.