what causes case head exspansion ?

[Willoughby]

what causes case head exspansion ?
and I'm assuming the case should be tossed at this point
thanks for any responces

 

[fredhorace77]

excessive headspace and also oversizing of brass

 

[CatShooter]

what causes case head expansion ?
and I'm assuming the case should be tossed at this point
thanks for any responces

Pressure causes anything that happens to a case. Don't toss them if the primer pockets are tight.

 

[fredhorace77]

as far as tossing them goes if there is a crack or the beginning of one at the web I would toss it. you can also use a paperclip to feel on the inside of the case bend a small L-shape on the end of the paperclip and file it to a point and you can reach inside of the case to feel for excessive separation. If you keep shooting them in this manner the case will eventually split and your bolt will just pull the case head out and the case body will be stuck in the chamber.

 

[Willoughby]

I noticed a few that are hard to fit into shell holder -primer pockets still ok
headspace .002
lapua brass -neck sized only after 1st firing
not sure what oversizing the brass means-too many firings? -5
just wondering what caused it & why its only happened on 2-3 case out of 100

 

[Barlow]

Too much gunpowder. Barlow

 

[spclark]

what causes case head exspansion ?
and I'm assuming the case should be tossed at this point
thanks for any responces

Case heads expand from the pressures they endure when rounds are fired. Brand new brass will tend to expand more than cases that have been fired before so I believe it's best to use new brass for reduced loads at first. This has the effect of 'work-hardening' the heads, the better to withstand full-power loads later on.

Some cartridge designs are more likely to suffer head expansion than others, and of course your rifle's chamber (generous diameter at the breech or a tighter, competition style) will have an effect too.

Yes, cases that won't fit the shellholder ought to be sent to the recycler rather than reloaded.

 

[jonbearman]

SP Clark,I have been telling a friend of mine to send light loads through new brass in his 35 wsm to work harden it alittle to do exactly what you said.He wont listen and looses cases to over expansion all the time .Thank you for bringing that up.

 

[fguffey]

Case head expansion, not recommended: A reloader can chamber an 8mm57 in a 30/06 chamber, then? Pull the trigger, again, not recommended. The case head can expand .040”, back to “What causes case head expansion?” When the case head is crushed it shortens, when the case head shortens it expands, at one time determining case head expansion was an art, today it is all about primers.

I have old tools that measure the diameter of the flash hole, problem, if the diameter of the flash hole is not determined before firing there is no information's that can to be gained by measuring after firing. Case head expansion is relative to an increase in the diameter of the flash hole, the increase in diameter of the primer pocket and the increase in the diameter of the case head at the bottom of the extractor groove, and, all of these factors results in case head thickness, back to ‘WHO MEASURES?’

Then there are other tools, a reloader, collector etc., called and suggested, in my travels, I avoid cases with certain head stamps, he suggested the cases would not fit his shell holders. I ask, “When did you discover the case would not fit your shell holder?” Before loading or after firing? Anyhow, he did not measure the diameter of the case head.

Case forming, a builder, reloader shooter/collector ask for help in forming cases for one of his wildcats, first I had to determine if it was possible without destroying too many cases. Then he ask me to bring the other shell holder for magnum belted cases, I did, with the dies/tools etc., I added a gasket cutting ball peen hammer to use when installing cases with case head expansion into a shell holder.

He had Weatherby cases, Browning cases and Winchester cases that would not fit his shell holder, we saved the ‘difficult to fit’ cases until last, before attempting to install in the shell holder I measure the case heads at the case ahead of the belt, the case had expanded .011” ahead of the belt, I measured the diameter of the case head at the bottom of the extractor cut, the case head had expanded .006” + at the bottom of the extractor cut. He decided not to use the cases that failed the shell holder test, I then suggested all shell holder are(were) not the same, he was using RCBS shell holders. I explained to him when developing loads there are shell holders that would not allow a case to be inserted long before having to give up using the RCBS shell holder, my favorite shell holder is the RCBS, it allows me for form case for short chambers, I form cases for up to .012” shorter than a minimum length length case, that is .017” shorter than a go-gage length chamber if the chamber is 30/06.

Then there are precision shell holders, precision shell holders will not allow me to get away with anything, there is no versatility built into the precision shell holder.

F. Guffey

 

[Barlow]

I,m pretty sure it was Ken Waters (and others) who used case head measurement to determine excess pressure. IIRC expansion of .0005 were reason for concern. Barlow

 

[bigedp51]

As stated above pressure causes case head expansion, and this depends on brass type and hardness. Example, military cases made at Lake City and civilian contract ammunition made for the military must be made from harder brass to withstand the larger diameter chambers and longer military headspace.

Below the main cause of case head expansion is high chamber pressure beyond the design strength limits of the brass.



Illustration from Varmint Al's

 

[Old Navy]

Too much gunpowder. Barlow

Ditto. Later! Frank

 

[fguffey]

I,m pretty sure it was Ken Waters (and others) who used case head measurement to determine excess pressure. IIRC expansion of .0005 were reason for concern. Barlow

I am sure you are correct, back to the first warning signs, it was suggested factory loaded ammo be used to establish a base line, normal case head expansion was .00025, then it got complicated, most reloaders do not have micrometers designed to measure a case head at the same place every time and it is suggested a different type of micrometer is necessary. Back to a case not fitting a shell holder, had the reloader measured the diameter of the extractor groove before and again after firing they would know the effect the load had on the case head when fired, again, my RCBS shell holders are versatile with room to spare, a case that will fit before firing and fail to fit after firing would indicate the case got hammered.

Then there is the other measurement, the case head thickness from the case head to the cup at the top of the case head. Commercial R-P case head thickness is .260” thick, military surplus Lake City case head thickness for the 30/06 is .200, case head crushing/case head expansion is normal, it is the amount of expansion that should be monitored.

F. Guffey

 

[expiper]

OP,,,case head expansion is caused by exceding the pressure capacity of the metal in the case head and also having excessive chamber dims. at the .200 line. If your chamber is oversize at the base circle even with normal or mild case pressure the brass can swell excessively and require oversizing and cause over working the brass beyond its elastic limits and bring about case head seperation and failure,,,,this is one of the most important things that is often overlooked in the proper and effortless functioning and reloading/resizing of ctgs....the ctg case and reamer/chamber and resize die must work in concert to avoid many of these problems..Roger

 

[Concha]

LOL...Big ed.

 

[jpretle]

In Guns, Loads and Hunting Tips, author Bob Hagel gives an excellant dissertation on measuring case head expansion. I am thinking he
is the one who developed the method.
At any rate, I use it and it works.

 

[bigedp51]

LOL...Big ed.

Your posting is "ambiguous" but you already knew this, get over yourself and stop your insults.

I hope you don't find the following "ambiguous", sometimes its simpler to quickly post a picture than mutable links with my two dyslexic typing fingers.

Benchrest Central
Case head expansion
http://benchrest.com/showthread.php?65270-Case-head-expansion


Case Head Expansion vs Peak Chamber Pressure
http://www.varmintal.com/arelo.htm#CaseHead

Finite Element Analysis (FEA) of a Remington Model 7 in 243 Win Caliber Using The LS-DYNA Software.
http://www.varmintal.com/amod7.htm

 

[CatShooter]

<---> "... and also having excessive chamber dims (??). at the .200 line. If your chamber is oversize at the base circle even with normal or mild case pressure the brass can swell excessively and require oversizing and cause over working the brass beyond its elastic limits and bring about case head seperation and failure,,,,this is one of the most important things that is often overlooked in the proper and effortless functioning and reloading/resizing of ctgs....the ctg case and reamer/chamber and resize die must work in concert to avoid many of these problems..Roger

The chamber dimension cannot restrain the case head expansion. If the chamber was tight enough to support the head from expanding, then you would not be able to chamber a round.

In the 308, the case head dia spec is is 0.4703" (-0.008"), and the chamber dia spec at the head, is 0.4714" (+0.002").

So the least empty space you will get with the 308 is 11 thou, and the most you will get is 21 thou.

So it is obvious that with between 11 thou and 21 thou, that the case head has no support of any kind... and when the chamber pressure exceeds the elastic limits of the brass, the head will flow outwards - i.e. expand.

 

[bigedp51]

<---> "... and also having excessive chamber dims (??). at the .200 line. If your chamber is oversize at the base circle even with normal or mild case pressure the brass can swell excessively and require oversizing and cause over working the brass beyond its elastic limits and bring about case head seperation and failure,,,,this is one of the most important things that is often overlooked in the proper and effortless functioning and reloading/resizing of ctgs....the ctg case and reamer/chamber and resize die must work in concert to avoid many of these problems..Roger

The chamber dimension cannot restrain the case head expansion. If the chamber was tight enough to support the head from expanding, then you would not be able to chamber a round.

In the 308, the case head dia spec is is 0.4703" (-0.008"), and the chamber dia spec at the head, is 0.4714" (+0.002").

So the least empty space you will get with the 308 is 11 thou, and the most you will get is 21 thou.

So it is obvious that with between 11 thou and 21 thou, that the case head has no support of any kind... and when the chamber pressure exceeds the elastic limits of the brass, the head will flow outwards - i.e. expand.

And don't forget the military doesn't use SAAMI figures and dimensions.