Case Uneven Wall Thickness

[Bart B.]

images.jpeg
The above image shows a once fired case with uneven wall thickness. Thinnest wall is where the pressure ring step is a few thousandths above the rest of the case head shown in the right picture. Thickest part is where no step is seen, left picture, same case.

Thinnest part of the new case neck is typically in line with the pressure ring max height. Cases with most uniform wall thickness end up the straightest after resizing. Seated bullet runout is typically best with such cases.

[Unclenick]

Roger Johnston and Merrill Martin used to call those "banana-shaped" cases, based on the bulged thinner side's greater runout.

The worst case I ever ran into was in the bulk Winchester brass I mentioned in another thread. I was using the NECO gauge with its anvil to measure the wall thickness runout back where the pressure ring forms. I found wall runout at that location was consistently twice as great as it was at the neck, so it gave me a more sensitive indication. One case out of the 500 I had in that lot measured a whopping 0.016" TIR, making it 0.008" thicker on one side than on the other. I confirmed the neck wall had 0.008" TIR, or 0.004" thick on one side than the other. That case didn't make it even into practice loads for concern over developing incipient head separation and gas leaks on the first firing. I still have it somewhere. I have no idea how something got that far off center in the forming dies, but apparently, it is possible.

[tangolima]

Were those 2 casings fired from the same chamber with exactly the same load? Is the pressure ring on the right brass evenly around its circumference?

-TL

Sent from my SM-G930T using Tapatalk

[Unclenick]

Not from what I see. It appears to be a crescent to me.

[tangolima]

Originally Posted by Unclenick

Not from what I see. It appears to be a crescent to me.

Then it indeed looks like due to uneven wall thickness. If the casings were fired from different chambers, one of the chambers could be slightly out of round.

-TL

Sent from my SM-G930T using Tapatalk

[Bart B.]

Originally Posted by tangolima

Were those 2 casings fired from the same chamber with exactly the same load? Is the pressure ring on the right brass evenly around its circumference?

Both pictures are of the same 308 Remington case. Check the head stamp orientation. 45.3 grains of IMR4895 over Rem 7.5 primer and a 155 grain Sierra used.

[Bart B.]

Originally Posted by Unclenick

One case out of the 500 I had in that lot measured a whopping 0.016" TIR, making it 0.008" thicker on one side than on the other. I confirmed the neck wall had 0.008" TIR, or 0.004" thick on one side than the other. That case didn't make it even into practice loads for concern over developing incipient head separation and gas leaks on the first firing. I still have it somewhere. I have no idea how something got that far off center in the forming dies, but apparently, it is possible.

Uneven metal hardness in the brass sheet doesn't coin, cup and draw to uniform thickness making the case wall thinner on one side.

Same reason bullet jackets of lesser quality are unbalanced.

[Unclenick]

That suggests they didn't anneal the brass before the initial strike. Or perhaps the particular piece suffered a handling problem.

[Bart B.]

Originally Posted by Unclenick

That suggests they didn't anneal the brass before the initial strike. Or perhaps the particular piece suffered a handling problem.

I had 500 of those Remington 308 benchrest small primer cases from the same lot. about 30 had uneven pressure rings after first firing, 6% of the total.

5% of my 1,500 WCC58 150 grain match cases had uneven pressure rings.

6% of the 92 PALMA cases had the same problem.

25% to 35% of Lake City 7.62 M118 match cases were the same way, but all had out of square case heads which would enlarge test groups up to 2/3rds MOA and therefore not worth reloading. No 'smiths ever squared up M1 nor M14 bolt faces

[Bart B.]

Originally Posted by tangolima

Then it indeed looks like due to uneven wall thickness. If the casings were fired from different chambers, one of the chambers could be slightly out of round.

Orienting fired cases in firing position put pressure ring high point all around the clock.

Few, if any, barrel or die chambers are perfectly round.

[Don Fischer]

I don't really get into tech stuff much, to confusing for me. Look's to me like the case on the right is preparing for case head separation! In those first pic's. Don't notice it as much in the other's but they are not focused very well. After running a case through an FL die, all I notice other than the separation if it is there is the difference in the case from where the die stopped to where it doesn't get to.

[Unclenick]

Don,

It's a split photo showing opposite sides of the same case. I didn't catch that right away, either.

[Bart B.]

Originally Posted by Don Fischer

I don't really get into tech stuff much, to confusing for me. Look's to me like the case on the right is preparing for case head separation! In those first pic's. Don't notice it as much in the other's but they are not focused very well. After running a case through an FL die, all I notice other than the separation if it is there is the difference in the case from where the die stopped to where it doesn't get to.

About 95% of all my good cases have very uniform pressure ring heights 360 degrees around the case. All new rimless bottleneck cases are a few thousandths inch smaller in diameter than the chamber 1/10th inch or so in front of the extractor groove. That part of the case expands to the chamber at peak pressure then springs back about one thousandth. The case at the groove and back to the case head expands only a few ten-thousandths. Full length sizing dies are larger in diameter at the pressure ring point than the last of several case forming dies used making the case from a flat brass disk

Incipient head separation does not happen. People have got 50 to 75 reloads per 308 Win case with max loads correctly full length sizing them setting shoulder back about .001" each time. That pressure ring is the same size and shape across all cycles. Case needs trimmed back a few thousandths every dozen or so cycles.

[F. Guffey]

I shooter, writer of gun reloated information and reloader purchased 500 cases from one case manufacturer. He did not assume but wanted to know if the cases qualified as good stuff. He sorted and resorted, he fired and re-fired and then wend back and matches the culls etc. When finish he found 47 cases that qualified as match/perfect cases.

And then he started over with the culls, some of the culls had powder columns that were not center meaning the case was thicker on one side than the other. And then he fired the culls by matching them, he found if he indexed the case in the chamber when firing the accuracy improved to quality cases.

I just do not have the nerve to claim any of his work as my own.

F. Guffey

[F. Guffey]

Incipient head separation does not happen. People have got 50 to 75 reloads per 308 Win case with max loads correctly full length sizing them setting shoulder back about .001" each time. That pressure ring is the same size and shape across all cycles. Case needs trimmed back a few thousandths every dozen or so cycles.

The first time this one went abound I asked you about the weight of the case when you started and the weight of the case when you finished. And now? You claim you trimmed the cases about ever 12 firings; so now the cases weighed less when you finished than when you started.

A friend died back in April, he was the one that build a custom rifle for a shooter that accused him of building a rifle with head space problems. I did not get involved, we were at the Market Hall gun show at the same table. The shooter and owner of the magnificent rifle pulled the case out and started telling the builder how bad the head space was.

Of course the only man in the building that could determine the length of the chamber without all of the shop tools was me. And then it was my turn, I asked the man with the bad case if that was the only case he had and I asked him if he was reloading it over and over and over etc. And it was about that time my old friend got up and asked to see the case again.

He suggested the shooter to a third part for another opinion. He was instructed not to tell the third part what I said and do not tell him who build the rifle. It was not long before the shooter came back 'mad', he said the other old man tore his case apart and measured the thickness of the case body. He said the old man told him .002" thickness is a good thickness for paper but not for case bodies. He then said the old man aske him if he was shooting that case over and over and over and he asked him if that was the only case he had.

I offered to form 200 cases for his custom rifle for free; he took what was left of his case and he never took the rifle to the shop to be checked.

F. Guffey

[F. Guffey]

images.jpeg
The above image shows a once fired case with uneven wall thickness. Thinnest wall is where the pressure ring step is a few thousandths above the rest of the case head shown in the right picture. Thickest part is where no step is seen, left picture, same case.

Thinnest part of the new case neck is typically in line with the pressure ring max height. Cases with most uniform wall thickness end up the straightest after resizing. Seated bullet runout is typically best with such cases.

Again for those that well again, I have gone to shooting ranges to purchased fired cases. It would be unseal for me to ever fire these cases again but I did not purchased the cases for reloading. I would go through there fired cases looking for cases that had been fired in trashy/ugly old chambers. I know and understand I am the only reloader that would do something like that because I am the only one that understands component manufacturers do not make cases for reloaders that know what they are doing. Component manufacturers manufacturer cases with one size in mind; they manufacturer cases that are minimum length/full length sized.

Minimum length sized cases are nice but I have chambers that have been around for 80+ years, through all of these years it has been assumed the chambers are go-gage length, it has been assumed all of the help at the arsenals were competent. And there were those that knew what they were doing. Again; I have a rifle with a long chamber from the datum/shoulder to the bolt face. The chamber is .011" longer than a go-gage length chamber. I could slap that chamber full of grease and fire off a round or two and all of that slapped in grease would have no effect on the case during firing when compared to a round that was minimum length sized/new over the counter.

I could spend the rest of my life talking about it but that would not change my mind about air, I am the fan of air between the chamber and case, what others choose to have between the chamber and case matters not to me.

Anyhow I use the case to off set the length of the chamber from the datum to the bolt face.

Back to sorting through cases at the range. While sorting cases I could match cases in groups of 20. I understand; what does that mean?

F. Guffey

[Metal god]

This once fired Winchester case may have that same issue . It is already showing signs the web stretching/thinning and fails the paper clip test . The thing is , it only fails it on one side . I forget the case weight of the top of my head but think they are in the mid 150’s . On vacation right now but when I get back I’ll pick up a dimal tool and cut it in half to see if it is in fact thinner on one side .

[Bart B.]

What is the criteria to fail the "paper clip" test?

a. Inside shoulder at pressure ring.

b. Inside groove at pressure ring.

c. Either one.

[Unclenick]

The only criteria I've ever heard is that if you can feel the dip as something as crude as a paperclip goes over it, it is time to toss the case. That said, some may use thicker paperclips than others, some may cut the paperclip with a wire cutter that results in a chisel tip parallel to the groove that has better sensitivity to finding the groove. No way to know.

I suspect the ideal tool would be a narrow hooked probe on a dial indicator that could tell you what size the dip actually was.

[Bart B.]

There are inside groove micrometers that could measure the case's pressure ring area inside shoulder height and groove (dip) depth to .001" or better precision.

I don't think a dip (groove) exists until the case body has been full length sized back close to the pressure ring and inside shoulder. Diameters of barrel chamber, case and die chamber matter as does case wall thickness and metalurgy properties.

[603Country]

Feeling for the undesirable groove, I use a length of wire heavier than a paper clip wire. It’s bent on one end, with about 1/4” sticking out, and I filed that bit to a fine chisel type edge that would be parallel to the groove. Works great at finding the evil groove. I found many incipient case head separations back when I had my 223 sizing die set up wrong.

[Metal god]

I sharpen the end of a short 90* bend in the clip . I drag that up and down the inside of the case body ( mostly ) around the web area . If the case is real bad it will kinda hang up in the stretched pressure ring at the web . I’ve been lucky enough or unlucky to have had a 300ct lot of brass that had several case head separations as well as good stretching at the web . This allowed me to test many cases at different stages of web stretch to compare them all .

You don’t want to feel anything as you drag the clip along the inside of the case body . Slightly stretched rings I can't really feel but if I feel the clip kinda dip in at any point I know there is an issue . If it hangs up a tad they are toast .

This is strictly a pressure and feel thing and I'm lucky enough to still have some bad cases to use as comparators ( or should I say headspace gauges ) I crack me up

[F. Guffey]

Feeling for the undesirable groove, I use a length of wire heavier than a paper clip wire. It’s bent on one end, with about 1/4” sticking out, and I filed that bit to a fine chisel type edge that would be parallel to the groove. Works great at finding the evil groove. I found many incipient case head separations back when I had my 223 sizing die set up wrong.

Bart B. claims the firing pin shortens the case between the shoulder and case head as much as .005" when the firing pin strikes the primer. If you get yourself a pencil you can add the total it up with the bolt slamming the round into the chamber. I do not work in the claims department but there are a few that do; they claim the case shortens as much as .007" when chambered and fired (and there is something/an event they always leave out) so the question is: How is it possible to prevent/avoid the case stretching between the case head and case body.

And then we have members that fire cases 45 times with maximum loads with no serious/ ill effects.

F. Guffey

[F. Guffey]

This is strictly a pressure and feel thing and I'm lucky enough to still have some bad cases to use as comparators ( or should I say headspace gauge ) I crack me up

If you were lucky you would luck into some experience and shop skill. Back to the problem: It happens but you do not know why, a reloaders that spends less time trying to be funny and making himself look good at others expense should be so luck as to luck into some shop skill.

And then there is this thing called 'the sequence of events'. A reloaders that has a problem should be able to look at/measure the case when determining the cause.

F. Guffey

[Bart B.]

Originally Posted by F. Guffey

How is it possible to prevent/avoid the case stretching between the case head and case body? (shoulder?)

Fire the rimless bottleneck round in a chamber with -.001" or -.002" head clearance.