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Measured headspace variation

 
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  #1  
Old 07-17-2010, 05:19 PM
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Measured headspace variation

Hi All, Im about to start reloading a Rem SPS in 7mmRM and have measured 20 once fired cases (Rem cases) that came with the rifle.I have used a Sinclair Bump Gage and find there is a spread of 0.003 btween the longest and shortest case. I have read it should be around 0.001 in variation.Why could there be such a difference.Is it the bolt,the brass,the previous guys ability to measure powder accurately or something else? The longest cases (8/20) do fit the chamber with no tightness detected. Do I leave my body die alone until they won't chamber or do I adjust the die down now 0.001 on the longest cases ? I have read that excessive resizing will lead to head separation so I dont want to over do things.The rifle is stock standard with no action trueing etc but I still want to extract as much accuracy as possible.
Any wisdom would be greatly appreciated.cheers Steven NZ
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  #2  
Old 07-17-2010, 05:39 PM
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Re: Measured headspace variation

You are checking them after removing the primers aren't you? Sometimes a slight crater on a primer will give you a false reading.
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Old 07-17-2010, 06:40 PM
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Re: Measured headspace variation

Doesn't sound like the brass is even fully fireformed to your chamber, much less ready for bumping.
Why worry about it till it's tight chambering?
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Old 07-17-2010, 07:10 PM
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Join Date: Jan 2009
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Re: Measured headspace variation

Hi,

Be aware two recent 7mm RM SPS rifles down here in Australia have what we believe are very poorly cut chambers. Chatter marks are evident on cases after firing and the owner has resorted to backing down 2 grains below max on the ADi manual which is on the light side., and even then he gets a binding bolt. Another fellow in our deer hunting organisation has the same problem with another SPS 7mm RM. Top Shot on this forum owns one of those rifles.

If its part of the batch that went down under you may have the same issue. IMO the reamer was no good .. 2 rifles in 12 months... Same issues in the same calibre
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Old 07-17-2010, 07:42 PM
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Re: Measured headspace variation

"...there is a spread of 0.003 btween the longest and shortest case. I have read it should be around 0.001 in variation."

What you read is someone's idealized dreaming, what you've measured is real world results. Variations of that magnitude happen within the same case lots because of small variations in the brass alloy even within individual cases, nothing we can do about that. Ditto the varaitions in the location of your resized shoulders.

It is NOT necessary to set resized case shoulders back at all. They expanded to fit the chamber and shrunk back at least a thou before you extracted and measured them. Just get your longest resized cases pushed back to the longest fired location and let the rest fall where they may.
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Old 07-26-2010, 04:22 PM
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Re: Measured headspace variation

Hi all , Thanks so much for your replies.Between your advise and the thread Titled "Belted Magnums Headspace on shoulder or belt" I now have a much better understanding on the sizing of my 7RM cases.Cheers to you all.
Steven
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