223 Case Rupture - Headspace Discrepancy?

[tangolima]

Originally Posted by mete

The HK G3 family has a similar 'problem' as the head moves back as the pressure is still high, causing the neck to grip at the same time, stretching the case .That limits the reloads to about six.

Passed 10 loads and still going here. Proper roller size is the key. Mighty strong Israeli military .308 brass also helps. I have a ptr91.

-TL

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[F. Guffey]

'problem' as the head moves back as the pressure is still high, causing the neck to grip at the same time, stretching the case .That limits the reloads to about six.

I believe we would be looking at another set of problems if that was true. I believe the limit to the number of firings would be limited to one because I do not believe the neck would still be connected to the case shoulder/neck juncture.

F. Guffey

[briandg]

This thread reminds me of another recent one. A member commented that his pistol cases grew shorter over time. It illustrates that there are many forces and actions. Pistol brass is worked pretty hard in loading, not so much on firing. Rifle brass is worked in entirely different ways, and imo, worked harder.

The gas op semiautomatic rifles yank the brass out by the base.

The long and short is that a solid action with neck size only, a properly fitted chamber, and realistic loads will will last until it won't hold a primer, o the neck splits. The brass isn't being worked significantly.

Reloading and using in a semiautomatic works the brass a lot more, and being a bit out of spec any direction will increase the wear a bit. Brass can only be worked a finite number of times before giving out, maybe catastrophically.

That's really all I have to say, is that reloading for one is obviously workable,
. My choice would be to use good brass and dump it after a few times. I'm really cautious.

Anyone can stretch that our many more times, but inspection well between rounds.

Btw, someone mentioned that brass was made by extrusion. No, it is drawn. There is a difference.

[Gunplummer]

Well Guffy, You would be wrong. I have used a ruptured case extractor many times (New brass) and never pulled just a neck out. All separation was below the shoulder. Somebody just had a Thread going about stretched brass(I think 7.5 Swiss) and it was the press doing it because the expander ball was too large. It really does not take much to stretch brass, especially if it is hot.

[243winxb]

Mine fired in Savage Axis The next round jams into the remaining neck in the chamber. Easy extraction. [IMG][/IMG] Brass washed in vinegar and in storage for a long time will get brittle and do the same thing. [IMG][/IMG] These fired in M16. Both my photos.

[briandg]

Using acidic cleaners for your brass? Neutralize with baking soda and then rinse very well to remove any residual metallic salts.

This is something to remember. Brass is zinc alloyed with copper down to the molecular level. It's far more complicated than mixing salt and sand.

Here is the reason I get rid of old brass. Tarnished, stained, corroded brass is breaking down molecularly. Zinc is separating, both metals are oxidizing, and the whole package is getting porous and weak, and once in a while it causes cases to fail. If any of you have ever fired REALLY old rounds and found that a number split, it is possible that the brass was just breaking down chemically to some degree. Any round that you find that's dark you can't recognize it as press and it has spots of green probably should be set aside.

[cryogenic419]

The 3rd picture in the first post sure looks like case head seperation.

http://bulletin.accurateshooter.com/...spot-problems/

[F. Guffey]

'problem' as the head moves back as the pressure is still high, causing the neck to grip at the same time, stretching the case .That limits the reloads to about six.

I could have sworn he said the neck grips the chamber and then I said if that happens I believe the neck separates from the case. But that is not what happens. The case expands and locks onto the chamber; after that it gets so complicated most can not keep up with it. And then there is that compulsory memory work; goes something like the firing pin strikes the primer then everything takes off for the front of the chamber including the bullet, case and powder and collides with the shoulder of the chamber. And then somewhere in there reloaders are trained to say; “and then the bang”.

A much disciplined reloader gave me 60 7mm Remington mag cases. It had nothing to do with not appreciating the cases but I wanted to know where he got the cases. Instead of answering me he wanted to know why I would care. I explained to him the shooter/reloader had some bad habits he needed to be aware of. The answer was “too late”, he died of a heart attack; point? His case necks were locking to the chamber. I had the cases and no one knew where the rifle went.

F. Guffey

[JeepHammer]

I'm not sure I run on F.Guffey's level, but I get what he's saying.

30+ years ago I was building/tuning AR rifles to better suit the rounds being fired through them,
and to this day eyes glaze over instantly when you start the conversation about gas pulse pressure AND duration combined with pulse timing.

Direct gas impengment firearms are MUCH more particular about gas operation than piston rifles,
But suprisingly, they are easier to tune in most cases...

It's no secret, the shorter the barrel/gas tube, the more issues you will have, both with operation of the rifle, but with the brass if you choose to reload, which isn't as widely known.

Short tubes will unlock that bolt LONG before it probably should be, and cause all sorts of issues, if not in the short term, it will most certianly cause issues in the long term by eroding bolts/carriers/gas rings, shaving/rounding over the locking lugs, and slamming that bolt/carrier to the rear WAY to hard...

Even in bolt rifles, way "Hot" loads will hammer the chamber out much faster than it should erode with 'Standard' pressure rounds.

[sirgilligan]

This is once fired PMC brass. Unfortunately I do not know which of my rifles it came from. I have a bolt, and very different semi autos. This is the first case I ever resized and pushed a bullet into. It has no primer or powder. I keep it on my desk. Its finish was all shiny and clean. After many months of picking it up and twirling it and fiddling with it as I sat at my desk the oils in my hand revealed this strange ring:



I ran a paper clip with a hook inside of it and there are no detectable edges or changes in the brass.

In my opinion it is just some type of change in the surface, either during extraction or resizing that allowed oils and dirt from my hand to work into that spot. I have other cartridges that are fully loaded from that same day that have not been handled and are uniformily shiny from top to bottom and look brand new.

[briandg]

I cant repeat it often enough. Get a jewelers loupe, twenty to forty, and keep a magnifying glass on hand, and get some reader glasses. You may be able to learn something about that particular shell.

I once got a package of Lake City brass in .308 that had cannelures at about that place...

[Gunplummer]

Jeephammer, You have just stated what everyone else is saying. Now try to explain it to Guffy.

[cryogenic419]

In response to Jeephammer's post.

Alot of the negatives could be quashed with an adjustable gas block.

Found out all about just how hard the gas system can beat up the gun and brass when I put a suppressor on mine. Dropped an adj gas block on there, found settings for shooting with and without the suppressor on there. Made quite a positive difference in the way the gun operates. No longer a massive pulse of gas violently unlocking the bolt and slamming the carrier to the rear. More of a gentle but effective push now.

[F. Guffey]

Well Guffy, You would be wrong. I have used a ruptured case extractor many times (New brass) and never pulled just a neck out. All separation was below the shoulder. Somebody just had a Thread going about stretched brass(I think 7.5 Swiss) and it was the press doing it because the expander ball was too large. It really does not take much to stretch brass, especially if it is hot.

'problem' as the head moves back as the pressure is still high, causing the neck to grip at the same time, stretching the case .That limits the reloads to about six.

I believe we would be looking at another set of problems if that was true. I believe the limit to the number of firings would be limited to one because I do not believe the neck would still be connected to the case shoulder/neck juncture.

Explain what? He said the neck locks to the chamber and I said it is not likely the case can be pulled apart while holding the neck. And then there is that story about pulling the shoulder forward with the sizing ball when the ram is lowered; and no one can measure before and again after.

F. Guffey

In response to Jeephammer's post.

A lot of the negatives could be quashed with an adjustable gas block.

And then there are pulse dampeners

[F. Guffey]

And then there is that story about pulling the shoulder forward with the sizing ball when the ram is lowered; and no one can measure before and again after

.

Well I exaggerated that one a little, I should have included the part about one reloader that can and has; that would be me, I can.

F. Guffey

[Gunplummer]

Yes! Gas regulator. Anybody that has owned an MAS 49/56 that was "Kind of" converted by Centry Arms to .308 knows exactly what we are talking about.

[JeepHammer]

Cryogenic,
I usually work towards a 'Lazy' full stroke of the bolt/carrier,
A gas restrictive block only limits the velocity the gas hits the bolt/carrier,
Tube length and powder burn rate determine the duration of the pulse.

Guys with very short barrels often used a longer gas tube coiled around the barrel to regulate pulse, and it worked pretty well,
But coiling that brittle stainless steel tube was a bunch of fun,
Ruined more than a few before I figured out how to do it...

The issue I have with most 'Aftermarket' gas blocks is they are made of high carbon steel, which doesn't hold up well to powder flame/temp erosion and dirty powder gives you something else with small passages/parts to clean...

I don't have all the answers, just been doing this long enough to form coherent questions...

[swmike]

I wouldn't use range findings on a bet. The only used brass that I would ever think about using would be commercial once fired from a good source.

Actually, I kind of like 'range findings'. I have a huge supply of LC brass I've picked up over the last few years at the range. Shooters leave it behind all the time because it has crimped primer pockets. That tells me that it's only been shot once and I get to process it for the first time.

I've paid for my Dillon Super Swage many times over and other than spare time I have absolutely Zero Dollars invested in my brass supply for my AR's.

Now if it doesn't have the original crimp intact, it just sits there with all the other crap brass that's left behind.

My bolt action gets a gourmet diet though. Nothing but Lapua Match and I buy that new.

On the original topic, when reloading people need to learn the benefit of a good case gauge or headspace measuring tool (tool, not gauge) when setting up their sizing die. Just cranking it down according to the included instructions will often lead to exactly the same type of separated cases shown. WHERE the break occurs is determined by what part of the case sticks in the chamber and what part moves when fired. Where the two parts meet is where the break occurs.

[mete]

I should have explained -the early tests by HK found indeed the case was torn in half !! Thats why the ,looking at a fired case , you see the marks of the grooves now cut in the neck and shoulder !! There are stains also from the escaping gas .This reduces the neck's grip on the chamber . You will find grooves even on a 9mm case from the P7 . The marks of the grooves are more coloring from the gas rather than grooves matching the chamber grooves.Yes I love my P7 !!

[tangolima]

The flutes in chamber are for such purpose. Spaniard greased their cartridges in their early versions of cetme. But It could still happen if the rollers are under-sized. With proper sized rollers, indicated by proper bolt gap, the brass can last as long as other actions.

-TL