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View Poll Results: Where's the case head when rounds fire?
Against/touching the bolt face as the extractor holds it there. 15 35.71%
Some thousandths off the bolt face; the difference between case and chamber headspacing references. 27 64.29%
Voters: 42. You may not vote on this poll

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Old May 19, 2019, 11:58 AM   #51
RaySendero
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Well...I think both "A" and "B" are possible.

I know "B" is possible.
Had an old Enfield that would have primers protruding from case head.
Saw these in reloads at the beginning powder steps.
Have reloads for a Rem M700 that I neck size, Bolt closes with some force.
So this rifle may "crush fit" with the case head against the bolt face.
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Old May 19, 2019, 12:03 PM   #52
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PS: I tried to vote both but wouldn't take it. Should have been a "Both" option.
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Old May 19, 2019, 12:46 PM   #53
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Bart B... I had to think long and hard about your question "is the case shoulder set back any amount from the force of the firing pin." I thought and thought. Then the light bulb went on!

I'm in no way a rifle marksman, but I am having fun learning to do better. Thanks for making me think about the whole system.
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Old May 19, 2019, 01:22 PM   #54
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I guess it depends on what the individual considers exactly when a cartridge is being fired? If you believe the process of firing starts when the primer is being ignited, then the case head is off the bolt face because the firing pin pushed it forward. If you believe the process of firing is when the bullet starts leaving the case neck, then the case head is firmly touching the bolt face.
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Old May 19, 2019, 01:40 PM   #55
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Does it really matter? Thinking more about this does it matter? Like most I have certain rifles I just enjoy shooting. One such rifle is a 308 bolt gun I built as part of a class maybe 25 years ago. The action wes trued and my barrel was trued. My finishing reamer cut was done using a Clymer pull through 308 finishing reamer. The finished chamber headspace was 1.632". I have checked the headspace over the years several times using a set of Forrester 308 headspace gauges pictured below. Years ago when I first bought these gauges I dragged them to work and checked them using an optical comparator and more recently these gauges were checked using a Zeiss CMM (Coordinate Measuring Machine).



Following firing, the brass in this rifle comes out right around 1.631" which would be my chamber minus 0.001". The rifle is heavy barrel having a 26" barrel length. My best groups with this rifle were right around 0.350" with 168 grain Sierra bullets. All of which is here nor there. All that matters to most average shooters is group size and the groups I mentioned were 5 shot groups at 100 yards.

New Federal Gold Match brass comes in around 1.629", I resize all brass for this rifle to a nominal 1.630" as using the RCBS Micrometer after checking it with my headspace gauges.

So looking at all of this, even discounting extractor clearance, the worst case scenario is my case head can only, at maximum be 0.002" away from my bolt face and the bolt face was lapped when I built the rifle. Even that opens another can of worms as how true a bolt face actually is in any given rifle? How flat is flat?

Finally how much does any of this really matter?

Ron
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Old May 19, 2019, 06:57 PM   #56
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Quote:
Finally how much does any of this really matter?
It's a good question because Bart did not give a reason as to why he asked a question he already knew the answer to .

I'll answer both , It matters A LOT ! ok that's one question answered , now for the why .

To know what is and what causes case head separation .



These cases were only reloaded 3 times . The problem was I was bumping the shoulders .008+ from fire formed from the same rifle that shot them . This resulted in excessive head clearance or the very thing we are discussing here . A large space ( in reloading circles ) left between the case head and bolt face when fired . This caused the cases to stretch in the web area more then you ever want . After stretching that extra amount 3 times the cases failed .

So why does the question matter . For me , to understand what's going on when you say internal ballistics .
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Old May 19, 2019, 07:33 PM   #57
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OK Metal God I can agree with that, in fact strongly agree. That said in my example I do not see where it matters. I can see where in your case and example it would matter. That really led to a short case life. As to the actual poll I haven't a clue what it was all about?

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Old May 19, 2019, 08:30 PM   #58
Bart B.
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Quote:
Originally Posted by Mike38 View Post
If you believe the process of firing is when the bullet starts leaving the case neck, then the case head is firmly touching the bolt face.
Most reloaded 30 caliber bullets we shoot need less than 300 psi in the case to start them moving in the case neck. I don't think that is enough to expand the case very much at all. Less than 200 psi in 22 caliber cases is enough.
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Old May 19, 2019, 09:37 PM   #59
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Bart,

Instead of us making up our own arbitrary definitions, as I and others have done throughout the thread, please tell us your definition of "when rounds fire" in the context of your question. Thanks.
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Old May 19, 2019, 09:42 PM   #60
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My tests with a Win 70's 26 pound striker spring pushing its near 3 ounce firing pin 9 fps into primed 308 cases set their shoulders back .003" to .007". Pin protusion normal at .060".
My test using a Savage model 10 and Ruger American and LC cases showed no shoulder set back by the firing pin strike . My guess is in your test you were also using those older Winchester cases that weighed something like 150gr meaning they were verey thin and likely it was likely easy to set back there shoulders ???? My LC cases weigh in the 185gr area , much thicker cases .
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Old May 19, 2019, 10:48 PM   #61
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BART B posted;
Quote:
My tests with a Win 70's 26 pound striker spring pushing its near 3 ounce firing pin 9 fps into primed 308 cases set their shoulders back .003" to .007". Pin protrusion normal at .060".
Your description of the test, is it 9 fps or is this 9 FP (Ft. Lbs)?

Here is an image of a cartridge misfire that i use in firearms Safety training.
Rifle used Controlled feed Ruger 77 MKII
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Old May 20, 2019, 06:10 AM   #62
Bart B.
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Originally Posted by Metal god View Post
My guess is in your test you were also using those older Winchester cases that weighed something like 150gr meaning they were verey thin and likely it was likely easy to set back there shoulders ???? My LC cases weigh in the 185gr area , much thicker cases .
Try basing your opinion on these facts.

I used new Federal and Remington cases about 170 grains and the pin speed was calculated to feet per second using lock time and travel distance.

Arsenal case shoulders are typically harder than.most commercial ones.
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Old May 20, 2019, 06:28 AM   #63
Bart B.
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Quote:
Originally Posted by Gbro View Post
BART B posted;


Your description of the test, is it 9 fps or is this 9 FP (Ft. Lbs)?

Here is an image of a cartridge misfire that i use in firearms Safety training.
Rifle used Controlled feed Ruger 77 MKII
Typical when firing pin doesn't dent primers at least .020 inch. Did you explain the different causes to the classes?

Feet per second abbreviates to fps.
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Old May 20, 2019, 06:44 AM   #64
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Quote:
Originally Posted by jmorris View Post
What were the components, measuring instrument(s) and techniques used in collecting your data above?

Protrusion and weight would be easy enough but striker velocity would be a bit more difficult unless simply calculated vs measured.

How much difference in set back is there between different manufacturers (cup hardness) or brass (annealed/work hardened/brand) or does the same thing vary .004 from one another?

I was assuming you were using just cases in the first example but your last post has me wondering how were you determining what happed to the fired rounds in the last post, since what happened the millisecond before pressure expanded the case to fit the chamber would be “erased”.
Calipers and case headspace measuring gauges were used for dimension measurements. Compression forces (weights) used to measure spring rating.

The harder cups are, the more case shoulders will set back. Harder case shoulders resist setback.
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Old May 20, 2019, 07:01 AM   #65
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That is intuitive, what were the components, measuring instrument(s) and techniques used in collecting your data above?
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Old May 20, 2019, 08:09 AM   #66
Bart B.
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Originally Posted by jmorris View Post
That is intuitive, what were the components, measuring instrument(s) and techniques used in collecting your data above?
How detailed do you want me to answer? I think my information would be understood by most folks familiar with this situation and the mechanics involved.

Have you measured your stuff to this level?

Will primers with less resistance to cup denting from firing pin will let the case shoulder set back less?
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Old May 20, 2019, 09:07 AM   #67
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I'm shooting a Rem700 with the standard ejector spring removed and a light weight spring installed to keep plunger flush with bolt face . Depending on how you size , if zero case space then for sure the case would be flush against the face but with case space it could be free to float one wy or the other the the extractor also comes into play.
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Old May 20, 2019, 09:18 AM   #68
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Wow, who think's up these question's? When the case is chambered the case head is in the same place it was before it was chambered. The separation of the case's in the photo show a few case's where there is to much slop in the action. The shoulder is back to far allowing the case to pull and separate. You can easily change the position of the shoulder by partial sizing. I doubt there's any way you can change the position of the head by sizing!
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Old May 20, 2019, 09:21 AM   #69
Bart B.
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Originally Posted by cw308 View Post
I'm shooting a Rem700 with the standard ejector spring removed and a light weight spring installed to keep plunger flush with bolt face .
Is the spring putting any force on the ejector with its tip flush with the bolt face?
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Old May 20, 2019, 10:55 AM   #70
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Bart B. there are reloaders that do not know and or understand where the clearance is: You have an absolute infatuation with clearance being between the bolt face and case head. There was a reloader near Gig Harbor that went as far as to set up an experiment to prove me wrong. He used Velcro to hold a 308W case in a belted Magnum chamber; he closed the bolt and pulled the trigger. Pulling the trigger did not bust the primer and then he used deductive reasoning to say I was wrong.

I did appreciate his effort; I thought he went way out of his way to disagree.

And now you have made a claim that you can determine where the clearance is located and you have claimed there is no way an extractor can hold the case against the bolt face and then you have claimed ‘if it did’ the extractor can not hold it ‘very good’.

And I have said I can check the length of the chamber from the shoulder of the chamber to the bolt face 3 different ways without a head space gage. And I have said even if I had a head space gage the head space gage will not measure the length of the chamber from the shoulder of the chamber to the bolt face.

Anyone/ a reloader that can determine where the clearance is located can measure the length of the chamber’ not really. Back to the day a friend build 4 magnificent rifles, when finished he went to test fire the first rifle. He had 5 case head separations out of the first 10 rounds fired. Not a problem but he was surrounded with a class bunch of smiths, He started out with; “He said they said…” That is a most difficult act to follow. I told him I could have determined if there was a chance his cases would suffer case head separation and I told him I could “FIX” the problem temporarily if he insisted on fire forming his cases. I form first and then fire.

He had another rifle that did not shoot groups; it shot patterns like a shot gun. I used home made tools to test the length of the chamber and the free fore. The throat was so long the bullet came out of the case long before the bullet got to the rifling. He asked me how that could happen. I explained to him he asked me to determine what was wrong with the rifle; first I told him “I do not know” and then I told him someone wanted more powder but did not understand what Weatherby was doing by increasing the length of the throat. ..

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Old May 20, 2019, 11:16 AM   #71
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And your point is??
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Old May 20, 2019, 12:14 PM   #72
F. Guffey
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Quote:
Well...I think both "A" and "B" are possible.

I know "B" is possible.
Had an old Enfield that would have primers protruding from case head.
Saw these in reloads at the beginning powder steps.
Have reloads for a Rem M700 that I neck size, Bolt closes with some force.
So this rifle may "crush fit" with the case head against the bolt face.
Well Mr. Fisher I can tell by your response you are not a 'YES MAN'. I have been saying it is impossible to move the shoulder back with a die that has full case body support; problem, finding a reloader that understands what that means. And then there are bumpers, they believe they can bump the shoulder back. All they need to be convinced they are correct is to have another reloader agree with them. It is not possible for them to understand what happens to the shoulder of the case when fired if they can not figure out what happens to the shoulder of the case when sized. the same crowd believe the case has head space.

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Old May 20, 2019, 12:33 PM   #73
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this is not the first time this question has run through a forum. I remember in the beginning when the popular beliefe was 'the datum is a line' and the rational for the datum line as given as 'and that is how they do it'. I claimed the datum was a round hole, I claimed the datum for my 30/06 case and chamber was 3/8"/.375" and that just locked them up.

And still? reloaders can not determine what happens to the case when fired. And then it got worst. Bart B. declared the firing pin drove the case forward until the shoulder of the case collided with the chamber shoulder, and then? THE BANG! And then he embellished the powder of the firing pin strike. He claimed his cases shortened by as much as .005" from the shoulder of the case to the case head.

And I thought, full length sizing to minimum length has a clearance of .005" befire sizing, when adding the abuse added by the firing pin strike we are left with .010" clearance. And now we add another question; Where is the case head after being driven forward by the firing pin strike and added to the clearance if the case was driven forward?

I understand, no one knows but if anything like that happen to one of my rifles the case head would be .010 from the bolt face. And I understand no one thinks that is a problem. Well not really everyone but not everyone is not a 'YES MAN'.

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Old May 20, 2019, 01:26 PM   #74
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Quote:
And I have said I can check the length of the chamber from the shoulder of the chamber to the bolt face 3 different ways without a head space gage. And I have said even if I had a head space gage the head space gage will not measure the length of the chamber from the shoulder of the chamber to the bolt face.
Yes, numerous times you have said that. However, you have never once explained how? I am sure, myself among them, inquiring minds would like to know how so please do explain exactly how you can do that three times without the use of a hardspace gauge?

Thank You
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Old May 20, 2019, 02:00 PM   #75
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Quote:
How detailed do you want me to answer?
As much as you would like to make it clear to folks with how you came up with your data.

Quote:
My tests with a Win 70's 26 pound striker spring pushing its near 3 ounce firing pin 9 fps into primed 308 cases set their shoulders back .003" to .007". Pin protusion normal at .060".
I can only assume how you came up with the above data if I don’t know if it’s something you measured or calculated, maybe both?

Quote:
One of my tests.... New Federal nickel plated 308 cases had their shoulders set back .008" with 38 grains of IMR4064 under 165 grain bullets. Primers were backed out about the same amount. New brass cases loaded the same had .004" shoulder setback.
How did you measure how much the shoulder was set back and primers backed out at the time of firing?

Were you just measuring a case and “firing” just a primer to get your set back data? If so did you drill out the flash holes? Maybe just made a primer inert and used it?

Was the .003-.007 just variations in brass, if so is that same lot or is that a range using different brands of primers?

If you can measure the above dynamically, what difference does seating into the lands make?

Anyway, without filling in the blanks we can only guess at what you did. We don’t need a PHD thesis but some idea of the tools an techniques you used. If you have instruments that allow you to measure real-time what’s happening to everything during the firing sequence you might have to go into more detail on equipment.

If it’s normal measuring tools/equipment just enough of a description where we could perform the same tests and gather parallel data.

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