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Headspace Variance

 
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  #8  
Old 06-24-2010, 12:34 PM
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Re: Headspace Variance

Wouldn't make a difference as the precision mic has a large hole at the bottom and it makes no contact with the primer.

Tom
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  #9  
Old 06-24-2010, 04:41 PM
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Re: Headspace Variance

"Seems like the explosion of the powder should conform the brass to the chamber dimension each time the same way irregardless of the brass."

It does, fully. But, you're measuring fired cases that have expanded and shrunk back a tad and your gage is showing you that some tads are greater than others; it's a good tool. You will also find simular differences after you ever so carefully FL size your cases, the shoulders just won't be at the same place each time, especially if you get sloppy and inconsistant with the press lever. Dealing with those small variations is part of life for reloaders.

Depriming before measuring will make no difference at all with that gage.

Last edited by boomtube; 06-24-2010 at 04:49 PM.
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  #10  
Old 06-25-2010, 06:42 AM
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Re: Headspace Variance

Holy $hit. Never thought about the brass cooling in the chamber. Man this is why I love reloading. Always something to learn.

Thanks for the lesson.

Tom
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  #11  
Old 06-25-2010, 05:55 PM
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Re: Headspace Variance

Quote:
Originally Posted by statjunk View Post
Never thought about the brass cooling in the chamber
IT'S SPRINGBACK
Seriously, you need to pick up a basic How-To-Reload book & read.
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  #12  
Old 06-25-2010, 07:53 PM
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Re: Headspace Variance

Quote:
Originally Posted by statjunk View Post
Hello All,

I have some fire formed brass that hasn't been put through a die yet and hasn't even had the primers removed.

I'm using a RCBS Precision Mic to measure the headspace and I'm getting a variance of 1.5-2 thousandths on the measurment between the brass.

How can that be? Shouldn't it be much tighter than that since it's fire forming to a chamber?

Tom
+1 on brass variations and springback could be one or both. How are you loading your fireform loads?? I have fireformed a couple of Ackley cartridges and I use the heaviest bullet for caliber I can find and seat it on the lands and use the fastest powder that I can find data (parent cartridge) for, for that bullet. Faster powder and heavy bullets (more bearing surface) will create more pressure and give you better finished brass. I have had no problems in fireforming hundreds of cases using this method. And yes I have taken all critical measurements after fireforming and they have been almost perfect. Quality of brass does help. Steve Timm a former gunwriter for VHM helped me out on my first Ackley and I have been using this method ever since.
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  #13  
Old 06-27-2010, 03:45 PM
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Re: Headspace Variance

Quote:
Originally Posted by Mikecr View Post
IT'S SPRINGBACK
Seriously, you need to pick up a basic How-To-Reload book & read.
Thanks Mike. Really appreciate your insight. I have read a reloading manual. To be specific Lyman 48. Just because you read a reloading manual doesn't mean you're going to remember everything you've read. Especially when you've read it a while ago. I could probably use a re-read but that it's going to be a while.

Tom

Last edited by statjunk; 06-27-2010 at 06:23 PM.
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  #14  
Old 06-28-2010, 07:07 AM
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Re: Headspace Variance

Wanted to provide some feedback on this issue. I was reloading for a friend when this issue came up. He has Federal brass from a 300WM. All his own fire formed cases with factory bought ammo.

I've never seen this issue come up in my rifles. I only use Nosler and Winchester brass. Never more than .001 variance.

I wonder if it's the powder or the brass causing this.

Either way I'll stay away from federal.

Tom
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