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How much shoulder bump?

You might want to use a .303 Brit cal Lee Enfield for your example since it is common for them to blow the shoulder forward .040 with new brass. They are pretty much the king of case head separating machines.

BoydAllen said:
I have seen new cases that stretched .006 when fired. While this sort of thing will ruin a case if done repeatedly the amount of damage done that one time has not been a problem. This is all in reference to a rimless case. The real surprise can be if you do a before and after measurement on a belted case. I encourage you to do that and come back with the results. Many years ago I knew shooters who were loosing belted cases after only a few firings. They chalked it up to "magnum pressures". The problem was that they were following the manufacturers' directions for setting their dies. If any of you have a belted magnum, some new brass and some fired brass, do a bit of measuring and post on this thread. As a reminder, we bump for only one reason, to create a little clearance. If we already have a little clearance, there is no need to move the shoulder. There is one thing that comes into this that some may not know. If you back off a FL die and adjust it down a little bit at a time, checking your shoulder to head dimension as you go, just before you get to the setting where the die comes into contact with the case shoulder the dimension will increase slightly over that of the fired case. This happens because of the sizing of the diameter of the body. Try it and see for yourself. That is why I recommend setting the die to a specific measurement rather than just backing it off so that the case is not bumped.
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BoydAllen said:
If any of you have a belted magnum, some new brass and some fired brass, do a bit of measuring and post on this thread.
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On my Rem Sendero 7mm Mag, using R-P brass, I get 0.011" growth of the case head to datum length on the first firing. And there is no bolt contact with that brass.
 
Bart B. said:
Regarding belted cases....... . . . . . .

Some have fired new ones testing loads at 1000 yards getting sub MOA results over 20 shots.

A few years ago, a 300 Weatherby Magnum set a 1000 yard benchrest record with virgin, new Norma brass:

http://bulletin.accurateshooter.com/2009/05/ken-brucklacher-sets-1000-yard-score-record-100-8x/
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Interesting. I wonder what their reamer drawings looked like. Back in the day, I was asked to spec out a reamer for a tight necked, no jump at magazine length .300 Weatherby. The factory chamber had the shoulder blowing forward about .021 when firing a new case. I reduced this to .006 which was little enough to not have any stretch issues but did give some advantage as far as doughnut formation. Of course we did careful pressure tests, since was no published data. It was a hunting rifle, built for long shots. The first time it was taken on a hunt after the rebarrel, it dumped an elk with a perfect shot. I forget the yardage, but it was respectable.
 
jepp2 said:
On my Rem Sendero 7mm Mag, using R-P brass, I get 0.011" growth of the case head to datum length on the first firing. And there is no bolt contact with that brass.
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On a factory 7mag, and .300 Weatherby, I have measured .021. The reason for this is that the SAAMI headspace spec is to the front of the belt and chambers can vary quite a lot to the shoulder, so they make the brass short enough to accommodate the shortest. Because of the belt, the case is blown forward rather than stretched at the back so it can take one firing with that much difference, but as you probably know, for sizing the die needs to be set up as if it was a rimless case, not as the manufacturer's instructions tell you to.
 
jepp2 said:
On my Rem Sendero 7mm Mag, using R-P brass, I get 0.011" growth of the case head to datum length on the first firing. And there is no bolt contact with that brass.
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If the case locked onto the chamber the case head has no choice but to stretch between the case had and case body meaning if the case increased in length between the shoulder/datum and the case head part of the .011" increase in length is a results of the stretch between the case head and case body.

Problem for the reloader is deterring the head space of a belted chamber. Again, there is a method and or technique that can be used to determine the clearance between the belt and chamber, knowing is more than a nice thing to know but I do not know of a reloader than has and or can determine the clearance 'in thousandths', I know, there are reloaders that have more than one gage. I am talking about measuring the head space on a belted chamber in thousandths , that would only require one gage.

F. Guffey
 
fguffey said:
Problem for the reloader is determining the head space of a belted chamber. Again, there is a method and or technique that can be used to determine the clearance between the belt and chamber, knowing is more than a nice thing to know but I do not know of a reloader than has and or can determine the clearance 'in thousandths',
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Allow me to introduce myself. I can do that. Others can, too. Measuring case head, belt or shoulder clearance is easy

I've measured all my belted case chambers' belt headspace with a new belted case, calipers and a cleaning rod. Repeated several times to less than .001" spread.

Remove the belt then use the same case to measure chamber headspace to shoulder and clearances the same way.

How, F. Guffey, is that possible?
 
BoydAllen said:
I wonder what their reamer drawings looked like.
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I think several used Henricken or Elliott reamers putting shoulder clearance with new cases around .005 to .007 inch. Thats based on chamber belt headspace at .220 and most good cases' belt headspace about .217 to .218.

A few thousandths clearance all over still let bullets center good enough for good accuracy.
 
I know a fellow that gunsmiths for a record holding 1,000 yard shooter who tells me that they have loosened up some fits from what they previously were, to good effect. Sometimes we think that we know things, so we do not test them.
 
BoydAllen said:
Sometimes we think that we know things, so we do not test them.
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I learned that decades ago. The gunsmith who built a lot of the most accurate NRA match rifles told me a 243 Win cartridge centered its neck perfectly in a 308 Win chamber when fired.

I didn't believe it, then he showed me how to learn why. He handed me the chamber section of a 308 Win barrel and a 243 Win case. It centered its neck perfectly in the chamber neck in the firing position. With a bunch of clearance all around its neck.
 
fguffey said:
I have made gages that check the length of the 30/06 chamber, I have 20 gages that include gages that go from .012" shorter to .020" longer than a go-gage length chamber. I have 30/06 rifles with chambers that are .011 longer than a go=gage length chamber.

Same for the 8mm57 chambers: I have found 8mm57 chambers that are .004" longer than a field reject length chamber.

At the same time I have friends that built wildcat that experienced case head separation on 5 of the first 10 cases fired. They always wondered why that happened on some receiver designs and not others. Anyone that cuts a chamber should be able to determine the length of the chamber from the shoulder to the bolt face. There are some simple methods and or techniques, problem, I am surrounded by reloaders that insist 'it can not be done'. One day, without a gage I offered to modify a no-go gage to measure 30/06 chambers from go to infinity. The man with the 20+ 30/06 gages thought that would make one of his gages a gage that was not 'period correct'.

F. Guffey
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Thankyou Mr FGuffey im now in the groove!!!
 
32971672-emoticon-farting.jpg
 
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