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Reloading Techniques For Reloading


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headspace question

 
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  #8  
Old 06-16-2012, 07:33 PM
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Join Date: Jun 2012
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Re: headspace question

Thank you for all the responses!

RE: the lengths i measured relative to SAAMI specs, i bored a healthy chamfer on the leading edge of the aluminum adapter piece that beds against the case shoulder, so i'm not sure at what diameter it contacts the shoulder at, and therefor not sure where the point i am measuring is relative to the base of the cartridge. it was more a tool to see where the cases are relative to each other (so i could control the amount i was resizing). maybe i should make another at .420 to see how i compare to the spec (suspect my chambers are on the extreme short end?)

my goal is to bump the shoulders back just enough to ensure they don't get stuck in the chamber. this hasn't happened yet, never had a sticky bolt on open or close on either gun. so maybe i don't need to worry about it? my goal is to develop sub moa hunting loads for different bullet weights, not exactly high accuracy by the standards of some.

I fired the 7RM brass another time today (2x fired total) and it did not expand further, so i must have found the end of the chamber.

facing the shell holder back so i can get the brass further into the die is a good idea, i'll give that a try.

the bolts are engraved with the last 3 digits of the serial # so i'm confident the bolts in both guns are original.

if anyone else has encountered this apparent short chamber or long die situation i'd be interested to hear about it.

thanks for the ideas, i have a lot to learn
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  #9  
Old 06-16-2012, 08:08 PM
Edd Edd is offline
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Re: headspace question

Got any plastigage? You might use a piece of that to see if you are close to contacting the die.
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  #10  
Old 06-16-2012, 08:30 PM
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Re: headspace question

Quote:
Originally Posted by ebsarg View Post
However, on both my rifles (sako 75 30-06 and sako 85 7mm rem mag) even when i screw the die all the way down all the way to the shell holder (at top of ram stroke) the location of the shoulder doesn't change.
Cases can take a few firings to fully expand to the size of your chamber. So if you are attempting to push the shoulder back after only one firing then you are not setting the die down far enough and you don't want to. You need to let the case expand enough to hit the shoulder before you start pushing the shoulder back with the die.

For example here are some measurements taken with a Hornady "Headspace" Gauge (even though not headspace on a belted case) with the proper insert that measures close to the datum line on a 300 win mag:

new case - 2.253"
once fired - 2.270" - neck sized with Lee Collet
twice fired - 2.272" - slight crush fit, neck sized with Lee Collet
3 times fired - 2.2725" - crush fit, push shoulder back

The point is that on the first firing the shoulder was still .0025" from expanding fully to fit the chamber. If you took a measurement on this firing and pushed the shoulder back .001" or .002" and decided that is your measurement and did it everytime, you would be forcing the brass to expand .0035" or .0045" every firing. This would accelerate thinning at the web, shorten brass life and possibly lead to a case head separation.

The best way is to chamber your fired brass in your gun and let it tell you when it is time to push the shoulder back.
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