Saum case fail

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Wal86
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Re: Saum case fail

#16 Postby Wal86 » Sun Feb 16, 2020 4:38 pm

When fireforming all virgin brass i seat into the lands and run a layer of tape or two depending on dimensions to support the rear of the case, and keep it central to chamber..
Just dont put the tape up too high or over lap the tape, think of it like a belted magnum.. Make sure you remove the tape after the first firing...


20200216_172500.jpg
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Tim L
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Re: Saum case fail

#17 Postby Tim L » Mon Feb 17, 2020 7:24 pm

So a bit of a doozy discovery to share with you on this, far easier than the paperclip challenge, gives a definite outcome and will do it a lot earlier than the paperclip. I think Peter will like this and can hopefully confirm my understanding of what's occurring.

I bought a cheap endoscope camera that plugs straight into my phone, just a cheap one off ebay. It's 5mm diameter and came with some screw on ends, a hook and a 90 degree prism. I was hoping to use it as a bore scope but the focal length is all wrong. It sat around unused for a year or so then this topic popped up.

I screwed the prism on and popped it in a case and,,,, not too bad, not great but picture you can work with. Unfortunately the prism has about 8mm of base that stopped me viewing the very bottom of the case wall where the separation occurs. Nothing ventured nothing gained, Dremmel in hand and, as luck would have it the prism stayed intact.

The focal length is still a bit out so the image isn't great but you CAN clearly see advanced case wall thinning. The picture on the phone is a bit better than the photos, not a whole lot but a bit clearer.

Now the clever bit (not that I'm clever, it happened by accident), If you line up one of the LEDs from the endoscope right in the middle of the image, when you put it in the case you get a nice reflection of the LED, but,,, if the case wall is starting to thin that reflection gets split into 2.

I've just gone through 200 6.5 Super LR cases. I've only had 1 actually split but it's the only gun that's given me one. I found 2 of the 5 x fired cases gave me a split beam but couldn't 'see' any groove. Of the cases fired 6 times, almost half gave a split beam with some showing the slightest groove.
20200217_182835.jpg

Single.jpg

Split case.jpg

Wall thinning.jpg


Peter, do you think this split reflection a definite indication of an undulation in the case wall?

If I try hard to angle the prism I can get a secont reflection into the image off the bottom of the case but it looks very different to this.
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Tim L
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Re: Saum case fail

#18 Postby Tim L » Mon Feb 17, 2020 7:47 pm

Tim N wrote:I.
The ring on the outside of the dodgy cases was a bit of a giveaway.


I don't put much faith in those external rings. I have them on nearly all my cases. I think it's just a witness mark showing the change from where pressure was applied to the case wall to where it wasn't i.e. the case head. I've checked loads of my 308 cases and , despite having the marks, I can find no indication of there being any case wall thinning. That said, maybe they become more pronounced as the wall thins.

Just a bit to add to the discussion over the actual cause.
I don't FL size and I don't bump my 6.5 cases. I got a Lee collet die from Lee custom. Since initially forming the cases, which is only neck and shoulder, the collet die is the only one they have been in. I have had no case growth either.
I do drive them hard though. For the results the rifle gives, 6 shot per case is acceptable. It's not bloody fantastic, but it's acceptable.

pjifl
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Re: Saum case fail

#19 Postby pjifl » Mon Feb 17, 2020 9:44 pm

Interesting use of a bore scope (endoscope).

I find it hard to interpret the pics. Maybe you can achieve a better focus by tipping the borescope sideways.
I have an optical endoscope which is not a 90 deg head. It looks forward slightly. Not the best in a normal barrel but maybe ideal in a case. I will have a look sometime. It is also focusable.

On the external stress ring - it tends to show distinctly when the thinning gets quite bad.

Some new shooters may confuse the ring with a rub ring caused by vibration when in a bullet box but I am sure that is not happening here.

I wonder if the stretch in an action is the cause of some thinning. The bolt and action locking logs are elastic at the pressures and forces involved.

Peter Smith.

DenisA
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Re: Saum case fail

#20 Postby DenisA » Wed Feb 19, 2020 9:51 pm

10ish years ago when I started reloading, I started with a .308. It was just a tactical type rifle that I was shooting at the SSAA trying to hit good groups at 100y. Purchasing my LEE FLS .308 Win die set and reloading kit was the first sign of the addiction taking hold.

The instructions in the LEE kit are rubbish and the way it instructs the user to set up the die basically bumps the shoulder back .020" from memory. It was huge. I didn't realise it was an issues to start with until I started seeing stages of incipient head separation at 5 firings. Conversations with Stuart E made me aware of that specific cause, LEE instructions and got me back on track only bumping shoulders 0.001" - 0.002".

The case in the picture is a Federal case and only has 5 firings on it. I've kept it and others.

The link below takes you to a YouTube video running this specific case on the RCBS Case Master tonight. Please take a look, its very illustrative and worth a watch.

I agree with using a paper clip or a scribe to simply detect thinning but no matter how many times I read this thread in a public forum, I can't bring myself to accept an assumption of the degree of head thinning to be an acceptable method of monitoring the issue if you are to keep running cases.

Its not just poor reloading practices that causes thinning, its also age of the brass if used for long enough. Brass flows forward as its worked, we keep trimming bits off the neck as it gets longer. The thicker walls at head is where it comes from. If your not running heavy loads, look after your brass, anneal, the primer pockets stay tight well then ultimately it will be incipient case head separation that will be the demise of the case. Point is, its normal to a degree and should be monitored and managed. I've had thinning in 6BR cases at over 30 firings. That example wasn't from poor reloading practice or over pressure, its was just general usage and brass flow. I never had a 6BR head split, but I was confident I could keep shooting them because I could see exactly how deep the groove was that I could feel with the scribe.

The result of getting this wrong could be CATASTROPHIC.

I find it difficult to comprehend that people will spend $1300 on scales to measure powder, $1300 on an instrument to measure MV, $1300 on a machine to anneal necks but when it comes to monitoring thin walls at the highly critical case head, an assumption will suffice. I stand by my advice that this something worth spending a relatively small amount of money on to get a MEASURABLE answer.

Please have a look at this video, its good in HD. You can see that towards the shoulder, the wall thickness is close to .017". As I travel down the powder chamber towards the head it thickens up. On the neck side of the thinned area we see about .030" and on the base side of the thinned area we see about .040".

https://youtu.be/1CT2DU0jhxQ

Tim N
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Re: Saum case fail

#21 Postby Tim N » Fri Feb 21, 2020 6:29 am

Great
Now I have to buy another doo hicky
Might not be a bad idea as I don’t have a good system to count how many times a case has been fired.
What systems do people used to keep count?
A mark with a file on the base is one way.
We don't rise to the level of our expectations, we fall to the level of our training. Archilochos 680-645 BC

Tim L
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Re: Saum case fail

#22 Postby Tim L » Fri Feb 21, 2020 7:12 am

I allocate cases to a barrel, generally 300 for a 308 but only 200 for the 6.5 and SAUM. I write 1 2 3 4 5 6 on the top of each ammo box. Once all the cases in the box are fired I cross off the next number and the cases get cleaned sized and annealed ready for reloading and I move onto the next box. That does rely on keeping the same cases in the same box but it also means each case gets tge same use. If I take the barrel off the cases go in Lapua boxes mark up with which barrel they're for and how many firings they've had so when I put the barrel back on it's just a case of tranfering the cases and info back to the ammo box.
If I'm not going to use the barrel again they all get full length sized and allocated to the next barrel but the info stays.

AlanF
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Re: Saum case fail

#23 Postby AlanF » Fri Feb 21, 2020 11:56 am

Tim N wrote:Great
Now I have to buy another doo hicky
Might not be a bad idea as I don’t have a good system to count how many times a case has been fired.
What systems do people used to keep count?
A mark with a file on the base is one way.

Tim,

I use a fine tipped marker and make marks about 2mm apart in the extractor groove. The first two are colour coded for the barrel, then the remaining ones show how many firings. I make the marks at each priming of the case. This can be very useful if you have a "castastrophe" with mixing up brass, as I remember happened to a mutual acquaintance at an airport some time back. However my method will not suit most shooters - I never tumble cases, which would probably remove the marks. The file marks could work, particularly if you could develop a precise method.

BATattack
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Re: Saum case fail

#24 Postby BATattack » Fri Feb 21, 2020 2:54 pm

Dremel with a cutting disc you can put a small notch in the case rim that won't be removed by tumbling

DenisA
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Re: Saum case fail

#25 Postby DenisA » Fri Feb 21, 2020 6:57 pm

Not saying this is THE way to do it. I load my brass in batches and keep each batch seperate. When I load each time I fill out a load spec sheet that amongst other info has the number of firings prior to loading. I have masking tape on the back of each box that checks off each time they’re fired and also worked. Then I also make notes in a barrel journal after each shoot. Sometimes I get lazy when I get home from the range and when I come back to the fired brass days or weeks or months later I’m lost. With 3 different parts to my system though I’ve always been able to remind myself of where I’m at with each batch or pile of brass.
Some times I forget to fill out the masking tape or the barrel journal but again it’s easy to work out with the all the info.

pjifl
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Re: Saum case fail

#26 Postby pjifl » Sat Feb 22, 2020 2:28 pm

I keep at least two boxes of projectiles to a barrel. Load one box while using the other.

Mark with a felt pen on box. One stroke when loaded, crossed off when fired. That way if you deem it worth sorting cases into an order, one keeps the order and they all fire an equal number of times. Some batches of cases benefit from order sorting.

On measuring case thinning, no doubt it is interesting and useful research but still subjective as to when to discard cases. I don't think there is any advantage over the scratch test.

Safety wise, the careful crafting of the chamber entrance by your Gunsmith is the most important factor.

Peter Smith.


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