Near miss probably dodged

[J.d. Popkes]

I've posted this many times but perhaps it bears repeating. This is how I avoid case problems for bolt rifles:

1. Start with virgin brass & dedicated to a specific rifle.

2. Rotate the use of the brass so all pieces receive an equal amount of firing and sizing.

3. Measure fire case head space with a bump gauge and adjust F/L die to zero bump. Often this is all that is necessary for the several firings. In my experience, it's the radial dimension that causes most of the chambering difficulty. The F/L die will solve that problem without repeatedly bumping the shoulder if the die is set up for zero bump.

4. Bump the shoulder only when necessary and only the amount necessary to achieve adequate chambering, usually .001 to .002 is all that is necessary for bolt rifles.

Yeah, I shoot virgin brass watching to see when it is fully formed and then size from there usually.002.

As far as I am concerned, the brass is worn out, used up. Is it me or are you lecturing me on how to size brass. This crap has been ran hard and I luckily caught it before it came apart. Why can’t that be the end of the lesson? I understand it’s been posted before. I’m not confused, I’m saying that it finally happened to me.

 

[K22]

Yeah, I shoot virgin brass watching to see when it is fully formed and then size from there usually.002.

As far as I am concerned, the brass is worn out, used up. Is it me or are you lecturing me on how to size brass. This crap has been ran hard and I luckily caught it before it came apart. Why can’t that be the end of the lesson? I understand it’s been posted before. I’m not confused, I’m saying that it finally happened to me.

I didn't mean to convey the post as a lecture. If I offended you, accept my apology. I have just read so many post on case problems I just wanted to share what I found that works for me. I might add that I am by no means an expert, I just have a lot of experience of making more than my fair share of mistakes.

In addition, my post was not necessarily directed at you, but at the wider viewers.

 

[Turkeytider]

Another illustration as to why I’ve made the decision not to get into reloading at this stage of life, all the while realizing that I’ll never know just how accurate I and my equipment might be.

 

[357Mag]

Happened to catch the one on the right, inspected with wire on some other ones, felt a ridge, looks like I best throw it away. View attachment 1758653

J. D. -

Howdy !


" Near miss " ?

Maybe.... more like a " near hit ".


With regards,
357Mag

 

[GetReal]

How many rounds on this batch of cases?

When I first looked at the case on the right I thought it was a belted Magnum.

 

[Straightshooter1]

I don't have a good drawing but I believe the .200" line and back to the case head is not in the chamber. More than you would think is outside the chamber so the extractor can grab the extractor groove. My guess is that has something to do with stretching and failure at this location. Maybe someone has a drawing showing how much case is outside the chamber?

Update:

just found this on internet:
In a typical firearm, the amount of the cartridge case that remains outside the chamber—often referred to as the unsupported case area—usually ranges between 0.110" and 0.160". This exposure is necessary to allow for proper functioning of the bolt, extractor, and feeding mechanisms.

In this picture, from the base to the .200" line is showing unsupported. When I measure the web thickness of this same case (base of case to top of a pin gauge) the thickness is .198". As can be seen in the pictures I've posted above, the cases are separating well above the .200" line.


Not only does bumping the shoulders back too much result in this stretching of the case body when being fired, it seems to me excess chamber wall clearance (or too much sizing) would do this too as can the sizing die squishing the body and forcing brass to flow upward and thinning the case walls.

 

[ELR LVR]

.200 line checker tools for sale here
Just sayin

 

[TA17rem]

yep they always do separate higher up. I'll digg few of my cases up .

 

[jimmymac]

IMO, too many guys want to blame shoulder bump for case head separation instead of looking at how much sizing is taking place all along the case after sizing and comparing that against a fired case. A good fitting die that closely matches the chamber negates many problems including case head separation. A poor fitting die that oversizes is not your friend. YMMV

 

[William Vogel]

Full length resizing which is what most of us do and what we should do to maintain consistency always reduces the diameter of the body of the brass. This action alone causes the shoulder and neck to push away from the case head. Even re establishing the shoulder to case head dimension of 0 headspace will cause the brass to stretch and thin towards the bottom of the brass near the case head. Every firing expands and stretches the brass. Generally the neck will crack or the primer pockets will loosen first but tight neck chambers and loads with reasonable pressure may keep these areas intact before the body becomes too thin. Careful resizing, tight chambers and reasonable loads all extend the brass life but the brass is expendable and is considered a wear item. It will wear out. If this brass only had a few resizing cycles, I’d say there was an issue but it appears from the post that it’s just gotten tired from a somewhat long term of service. I have 223AI brass that’s been sized 20+ times and I’m sure it’s about to expire but I’ll keep using it because it saves me the trouble of fire forming the other inconsistency issues of new brass. It takes about 300 bullets and primers to get the 100 new brass to settle into the chamber. I prefer to keep shooting the “good” brass than to start over again before it’s time. Kinda like those old blue jeans that are thin and worn but man they fit perfectly for doing stuff around the house. The knee or inseam will rip at some point but I’m wearing them until it happens.

 

[William Vogel]

A common mistake many people make in setting up a sizing die for shoulder bump occurs when they measure a fired case and then set the die to bump the shoulder to either the length of the fired brass or just a thousandth or two under the length of the fired case. The fired case doesn’t really represent the headspace of the chamber and usually won’t fit easily into the chamber before sizing because of the body and neck dimension after firing. Depriming and measuring a fired case usually creates a dimension that is short and bumps the shoulder excessively. The headspace of the chamber needs to be realized to properly establish shoulder bump. It can be accomplished with a piece of brass or a headspace gauge a clean chamber and a disassembled bolt. Once the bolt closes on the “gauge”, use Scotch tape to add shim to the gauge. When the gauge just becomes too long to close in the chamber, you’ve just about established the headspace. The Scotch tape is very close to 0.002 thickness. Removing the last shim of tape should again allow the bolt to close on the gauge. Measure the gauge with your comparator setup and write this dimension down. This is now the dimension you should reference to set the die. You can now bump a piece of brass 0.001 longer and check that it fits the chamber by closing the bolt. If it fits, you are now to within 0.001 of your true headspace and you can decide how much shoulder bump you want for your brass.

I’m sharing this because I’ve found that once or twice fired new brass doesn’t provide a true reference for headspace and generally produces a shoulder bump that is excessive and that many people measure the fired case, begin adjusting the die to get a bump based on that number and yes the brass chambers. Take a piece of tape and shim that brass just to confirm that it’s not too short.

 

[Janeau]

Brass have a finite life. Not keeping track of number of firing and just reload them over and over will bring this kind of failure. Don’t cheap out. When you start to get that in a lot - dump them all and start new.
With time you will really know how many firing it take for your case to be tossed. In my M1A in .308 - 4 firing is the max - in my Cadex .308 bolt action match chamber - I can get 8-10 firings if primer pocket last.
Keep in mind brass brand is a factor also..they are not created equal.

 

[J.d. Popkes]

It likes its new brass as good as the old stuff I had to toss. Did a couple 5 shot groups at 600 both 1-3/4”ish. Low sd-es. All is well, but I’m going to be more vigilant, concentrating on this

 

[TA17rem]

Here is a few

 

[davidjoe]

You may know this, but for those who don’t. That comes from pushing the shoulder too far back on your brass, and too far back, doesn’t take much over the course of a few reloading’s.

Every time you fire a case, the firing pin drives the case to the front of the chamber, the sides expand grip the chamber, and then the bass expands to meet the bolt face and it stretches in a 308-based case where you see that one or maybe even a little further back, and on 223 it’ll happen a little further forward.

So if you push your shoulder back 4thou each time you resize when you shoot it four times it stretches ~16, though usually it’s bumping back about 10 thou+ that gets you into trouble. Multiple chambers not cut with the same reamer is another commonality.

I’ve had small primer Lapua 308 shot at full up FTR loads for so many reloads I lost count. In 10 yrs of competition (my reamer on all barrels) I think I split one neck, the rest of the brass I threw out to loose primer pockets. Never had a case head separate. Not that I have’t had one, just not with brass sized for the chamber. I bump right at 2thou. To be consistent at that close you need to anneal.

@markm87 measure his fired brass. One of his chambers is longer than the other. Need to sort till he can get two matching chambers.

I follow the thinking here, but I think the opposite process explains the weak spot.

Your explanation of the case’s side gripping the chamber wall would mean that the “revision” of improved fire-formed brass all came from the unsupported region of the brass, which ought to create its own distinct ring.

I think it would also imply that there is some exact level of powder charge you could select, where a cartidge could be set off in a just a chambered barrel, grip the chamber wall, and stay in there. That would be the implication of the unsupported area really being able to move rearward relative to the rest of the case.

Obviously that’s not something to try to ascertain, but I would think that at or under proof it is all coming out, meaning only the bolt face stops it from coming rearward.

So, once the bolt face stops the case head, and there is unnecessary length in the chamber, then, the “rest of the case” that is NOT the case head, (because it can’t) starts moving to fill that gap, stretching forward and bigger, similar to inflating a balloon that cannot move rearward.

The movement from pressure that is relatively uniform inside the case (necessarily), repeatedly finds and thins out the same weak spot in resized brass, which is not necessarily the unsupported point of the brass, but sometimes well into the fully supported area.

 

[XTR]

Most people fire form with either a hard jam or a false shoulder, in both cases to prevent forward movement of the case.

 

[Webster]

Case separation, one of the reasons I don't pick up other people's brass at the range..

I would assume most range pickups have only been fired once. Especially 9mm and 223.

 

[J.d. Popkes]

My virgin brass grew .003 on first firing so that’s perfect. I’ll size minimally and go from there.

 

[Webster]

Happened to catch the one on the right, inspected with wire on some other ones, felt a ridge, looks like I best throw it away. View attachment 1758653

I wonder why you get case body separation near the back 1/3 of the case, never the front 2/3. What's going on? Seems like the same location on most pix on this website. Why would the max case stretching occur in an area less than a 1/16” wide. You would think the stretching would occur uniformly over a wide area????

Never had a case separation in 55 years. Is it some match up of chamber size, die size, bumping too much and hot loads. We may never know.

 

[davidjoe]

I wonder why you get case body separation near the back 1/3 of the case, never the front 2/3. What's going on? Seems like the same location on most pix on this website. Why would the max case stretching occur in an area less than a 1/16” wide. You would think the stretching would occur uniformly over a wide area????

Never had a case separation in 55 years. Is it some match up of chamber size, die size, bumping too much and hot loads. We may never know.

I imagine that the weak spot is going to be the area of the case body where it gets both narrowed down the most by a sizing die, and then expands the most on firing.

Somehow working that material makes it both brittle and thin. Brittle is easy to understand. But working metal makes it thinner too. This was first learned bending a paper clip back and forth out of classroom boredom.

I do not know exactly why it gets thinner where you bend it back and forth, probably the stretched material never fully returns, but it most assuredly does. It gets weaker, thinner, softer, longer, and then falls into two fairly pointy pieces as you work that area, and I surmise the same thing happens from the body die. Not from any shortening of that area by way of pressure exerted to bump the shoulder, but from narrowing it, (which squeezing not only mechanically narrows it, but necessarily lengthens it, which cannot happen without it becoming thinner as well, somewhere, the weak spot I’d imagine, which is a second process that might explain the sharpness of the thinning out we see in a ringed area.

Together, they may explain an area of gradual thinning, from working the brass, that transitions to a short, distinctive ring of dramatic thinning caused by “stretching” that finds the weakest part of the overworked area, and all occurs there, both externally from the sizing die and internally from case pressure to both re-widen and re-lengthen the body.