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Old June 24, 2011, 04:14 PM   #1
bow shot
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make me understand: case expansion

This intrigues me:

I'm presently only neck sizing, and have reached the point (7x fired) where my loads are just beginning to cause slight resistance to camming my bolt handle down (yes they are trimmed at or below spec., and they eject without any unusual labor).

The thing that make me go hmmmm is this: If these cases expand to my chamber's dimension and then spring back a tad each time they are fired, isn't that akin to running them in a custom sizing die each time I shoot... ie., my chamber? How then does the brass end up "too tight" after being fired if the trim length is good, and it "shrinks back" a tiny bit after firing?

I'm all ears...
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Old June 24, 2011, 05:45 PM   #2
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Quote:
How then does the brass end up "too tight" after being fired if the trim length is good, and it "shrinks back" a tiny bit after firing?
Because the case brass slowly (but inexorably) flows forward under the pressure of a open-ended rocket engine...

(`Told y'all this was rocket science, ...right?)
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Old June 24, 2011, 05:58 PM   #3
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Quote:
The thing that make me go hmmmm is this: If these cases expand to my chamber's dimension and then spring back a tad each time they are fired, isn't that akin to running them in a custom sizing die each time I shoot... ie., my chamber? How then does the brass end up "too tight" after being fired if the trim length is good, and it "shrinks back" a tiny bit after firing?
Did you notice that although the cartridge is getting more difficult to close/lock the bolt on after several firings, after you fire the cartridge, it seems to come out of the chamber (and will go back in the chamber easily empty also, as long as you do not size the case), without undue effort?
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Old June 24, 2011, 07:09 PM   #4
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When fired it forms to the chamber perfectly, then you remove it reload it & try to rechamber it in a "inspec" chamber which in fact has tolerences & these tolerences no matter how small will cause fit issues .

Now if you indexed the cases so they could be inserted into the chamber in the same orientation may help , but still considering the neck sizing process & seating the bullet will still cause problems .

I personally try for .005 shoulder set back with a FL sizer to insure no troubles .

You may also benefit from checking to see how each step of your process affects the case by trying to chamber 10 cases after each step & maybe change the process abit to aleviate moving brass the wrong way .
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Old June 24, 2011, 07:40 PM   #5
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Ok, got the replies, thanks folks, so here's my re-re's:

mehavey:
got it... but the case length when I extract is still good (under trim length spec.). Am I making sense??

dahermit: yes, they extract fine... but I'll have to check an see if the ones that go in a little tight are still tight after siring. I'll do that tonight.

GP100man: great idea in that last paragraph. Funny, I've given others the same advice, LOL! I guess I didn't do that this time is because It just happened the other day and I haven been back to the reloading bench yet...

More to come!!!
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Old June 24, 2011, 07:45 PM   #6
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Your brass work hardens a bit more every time you fire it. When it gets work hardened its ductility and spring back is reduced. It's inevitable that eventually it will not spring back and become hard to extract. Annealing will definately help and it extends the life of the brass.
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Old June 24, 2011, 09:57 PM   #7
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+1 what flashhole said
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Old June 24, 2011, 11:01 PM   #8
F. Guffey
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Fire the case to fire form, then neck size 5 times and start over, that does not make sense to me either, when I fire a case 6 times it has been fired 6 times, that goes right along with the case is not fully grown until it has been fired 5 times, never a mention as to what chamber, never a mention as to trimming, never a mention of the weight of the case before it was fired the first time, never a mention of the weight of the case after 6 firing.

Then there is stretch and or flow and all that hammering. When I hammer on brass it yields, flattens, and flows.



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Old June 25, 2011, 03:15 AM   #9
mehavey
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Quote:
1. but the case length when I extract is still good (under trim length spec.). Am I making sense??

2. yes, they extract fine... but I'll have to check an see if the ones that go in a little tight are still tight after firing.
Doing #2 is a check on whether #1 is true in fact.

By definition, cartridge cases (unlike children) don't grow by just sitting around. What's tight going back into the chamber was actually tight when it came out of the chamber.
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Old June 25, 2011, 10:49 AM   #10
bow shot
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Yup, trim length is steady, and fired cases chamber tight, slight resistance as the bolt is cammed down.

mehavey: Understood, thanks! I'm thinking at this point then, that since trim length is steady, then this must be shoulder enchroachment

flashhole: I think you nailed it!! Great intel right there. Sounds like time to anneal and shoulder bump.

'Guffy: Here are the vitals:
Savage .204 ruger VLP bolt (appx 1,000 rounds)
Nosler brass
7x fired, neck sized after each firing (therefore 7x sized)
Brass weigtht is 99.3 - 100.4 gn within 50 pcs, at initial weigh-in (after 1st firing), and consistent through all firings (@ 99.4 -100.6gn, I'm associating that to burn powder residue that stays after tumbling)
VLD chamfered
no flashole prep
No trimming at all, 1.838" +/- .002"
Fed small BR primer
Benchmark powder
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Old June 25, 2011, 01:14 PM   #11
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If one fires bolt loads to excessive pressures, hard bolt lifting and sticky extraction are typical symptoms. What happens in this extreme case is the result of the true elastic limit of steel (the stretch from which it can return 100% to original shape) is higher than the true elastic limit of brass, which is pretty low. The chamber expands and the bolt lugs stretch back, allowing the brass to get bigger than the cold chamber was. When the steel snaps back to shape, it then traps and compresses the now-oversized brass. That compression causes the friction the bolt lifts and pulls against.

In loads that are not excessive, the same thing happens, but to lesser degree. The steel still stretches (that's what a strain gauge pressure instrument measures), so the brass is still allowed to get a little bigger than cold chamber size during firing. It just isn't allowed as far beyond its elastic limit as it is when the pressure produces sticky symptoms in a single firing. It then takes a larger number of firing cycles for the accumulated stretch to resist chambering. But unless the pressure is so low even the true elastic limit of the brass is not exceeded, eventually it will. Some light handgun target loads below around 10,000 psi are like this.

There are other factors involved. A lot of factory guns need their bolt lugs lapped when they are new. You can get the stretching problem while the lug not making contact stretches back to touch its receiver lug. This makes the whole case stretch thing happen at lower pressure than it would in a gun with solid lug contact all around.

Another factor that is all too common was hinted at in a previous post, and that is imperfection in the coaxial location of the chamber and bore. In other words, the chamber is slightly tilted off the bore axis. That's where rotating the case with respect to where it was when it was extracted will cause it to feel tight in one orientation before it does in it original orientation. An out-of-square-under-pressure bolt face can cause the same thing.

But eventually, even in a smooth and perfectly bore coaxial chamber and with a properly squared bolt face, brass will normally get tight both going in and out. The only way it won't do that is if the pressure is below even the elastic limit of the brass.

A lot of the benchrest guys will neck and body size separately. They get a custom die blank cut with the same reamer used to cut their rifle's chamber. The depth of the cut is limited so the die will still push the shoulder of a fired case back a thousandth. They say that a allows a little self-centering of the cartridge to occur that improves accuracy over firing a case that is neck-sized alone. It's a way to avoid the case ever getting too tight, too.
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Last edited by Unclenick; June 26, 2011 at 10:41 AM. Reason: typo fix
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Old June 25, 2011, 09:13 PM   #12
bow shot
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!

As usual most excellent, Unclenick!
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Old June 26, 2011, 11:35 PM   #13
F. Guffey
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(yes they are trimmed at or below spec., and they eject without any unusual labor)

Savage .204 ruger VLP bolt (appx 1,000 rounds)
Nosler brass
7x fired, neck sized after each firing (therefore 7x sized)
Brass weigtht is 99.3 - 100.4 gn within 50 pcs, at initial weigh-in (after 1st firing), and consistent through all firings (@ 99.4 -100.6gn, I'm associating that to burn powder residue that stays after tumbling)
VLD chamfered
no flashole prep
No trimming at all, 1.838" +/- .002"
Fed small BR primer


The 204 case length could be 1.850, yours are 1.838, and the case has not lost weight, trimming a case during 7 firings could result in weight loss, I would not think a cake build-up would off set the loss, I do not know, then there is the hammering effect, compression or yield of brass, again I do not know but it seems you have that workout also.\\There are a few actions that jump apart and then snap back together, the first one that comes to mind is the British type 303 then there are brake overs then there is this firing a case 7 times then return it to start over condition by full length sizing, I do not know about that one either, the one I do know about is the one where the case grabs the chamber and locks onto it with the head of the case not resting on the bolt face, with the case body locked and the head of the case jamming itself against the bolt face and in order to do that something has to give, if any of that is true and there is no recovery, memory or spring back, the head of the case could be causing the case to wedge between the head of the bolt and chamber body, but without knowing the diameter of the case head and diameter there is no way to determine.

Your cases are not loosing weight due to trimming, your cases are not getting longer, seems you have it under control, not me, after firing a case 6 times it has been fired 6 times and, I find it impossible to start over, my cases get hammered, my cases yield, most of them have no memory of what they were before I fired them.

Steady or stable?

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Old June 26, 2011, 11:58 PM   #14
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If I resize a .223 case in Redding FL "S" die and then in a honed Forster FL die, neither with expander balls, the case grows more in length than if I do it in the other order.

I have not figured out why, but I have figured out how to stop trimming brass, don't push the shoulder back every time, and if I do, only .001".
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Old June 27, 2011, 12:02 PM   #15
bow shot
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about that trimming...

'Guff: I should add to my "no trimming at all" line, that they veryl likely have grown, but I've only monitored them, and ensured that they've not exceeded the max trim length. I do remember that the Noslers were remarkably short right out of the package, and actually got a tad shorter after the first firing.

Steady or stable? At this point its more like "halted", LOL!!

Clark: I'll likely go the anneal and then bump rout (just ordered a redding body die) , rather than adjust with a FL die for these two reasons:

1) I know what to expect for neck ID out of my neck sizer and dont' want to change it (I was stupid enough to sell my FL sizer when I went to neck only: ignorant)

2) I don't want to throw the brass away, and figure I've got little to loose by at least giving it (anneal/bump) a try ($29 for a body die).
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Old June 27, 2011, 07:22 PM   #16
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What Nick said plus----------

The Forster neck/body die can be used to reset the case to a usable size while still allowing the least brass flow attainable in today's dies and so extend case life to some extent. I've found more hard extractions and chamberings due to high shoulders than to case head expansion..........In some cases that may not be enough. I have found though experimentation that the Redding small base body/shoulder bump dies are best for some cartridges I use. Ideally I would have known this before and bought Reddings small base "S" dies, but life is full of such calamities. Some day if I win the lottery I will buy a reamer or two and have all my chambers made to the same specs as my FL bushing dies...............
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Old June 28, 2011, 07:44 AM   #17
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I think GP100 got it... the more times a case is fired, the less elastic the brass gets. This equals less spring back, meaning that the shoulder of the case does not spring back as far from the chamber. It's becoming a "press fit" against the shoulder of the chamber. Try setting the shoulder back about a thousandth or two, see if your loaded cartridges don't just slide right in with no resistance on the bolt.
This problem is usually seen in rifles that have more "flex" in the action, such as the T/C Contender. The action flexes just enough during firing to allow the case to form to the chamber without springing back as much. After several firings, the action is a little difficult to close with some brass. Bellm wrote the definitive article about Contender actions and "flex"...

Annealing the neck/shoulder should help somewhat, as well.
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Old June 28, 2011, 11:08 AM   #18
bow shot
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Ordered a redding body die yesterday... I see that I may have to buy the comp shellholder set too. gag:barf:... It seems everytime I find a cheap, solution, it ends up getting expensive.. when will I ever learn....

Well. I understand the issue now, and that's priceless... and the knowledge gained here was free. God bless the Firing line Brethren!
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Old June 28, 2011, 03:52 PM   #19
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"... I see that I may have to buy the comp shellholder set too"

A member of another forum did just that, he purchased the Redding Competition shell holder set, the experience almost locked him up, I had suggested he purchase a feeler gage for $11.95 to use as a companion tool tool his press, I tried to explain to him Redding does not make shell holder for short chambers meaning the competition shell holders are designed to be used to off set the effect of head space in the chamber when the case is fired, am impossible concept for most reloaders to grasp.

Again, the feeler gage can be used to size cases from -.012 thousands (short chamber) under a minimum length/full length sized case to + infinity. I was at the Big Town Mesquite gun show last month when I found a #6 set for magnums, $5.00 dollars, of the 5 shell holders 3 were off by .001 each, for me, no problem, the feeler gage turns my standard RCBS shell holder into a competition shell holder from .000 to .010, that is 10 options for the same price of the feeler gage, the Competition shell holder set cost about $40.00.

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Old June 28, 2011, 04:15 PM   #20
bow shot
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funny you shlould mentoin that...

... I just grabbed my work set to borrow as I head out the door to go home. I don't have the Redding die yet, but I'll be tinkering. 'Glad to know someone with good intel thought of it, makes me feel better.
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