Musgrave 243 with oversize chamber - fire forming tips to avoid case stretch?

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Oct 6, 2012
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Hi, I have a 6mm/243 with a slightly oversize chamber (headspace on fire formed brass measures 41,02mm as apposed to the more regular 40,96mm). When firing cases, the additional headspace leaves stretch marks on the cases (similar to excessive pressure). I am worried that these cases will eventually suffer from case head separation. Any ideas on how I can fire form new brass to avoid this issue? Any help/advice will be greatly appreciated!
 

royinidaho

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Jan 20, 2004
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Blackfoot, Idaho
When fire forming from a shorter base to shoulder to longer base to shoulder length while reducing the caliber, say .284 to .277 it is common to only partially size the neck leaving a "ring" to head space against.

This procedure ensures no case stretching when fire forming.

How to duplicate this process where you are not reducing caliber is the question.

Maybe size w/7mm-08 die then partially resize with 243 die? Not certain of the best way on this one....
 
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Oct 6, 2012
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One question Royinidaho...
The 243 and 7-08 share the same parent case and therefore headspace? My problem is headspace and not necking down. What case would be the next size up (i.e slightly longer headspace, but still 08 diameter) from a 243, with a bigger neck size? But still being able to size down to 243? Cause I think it's a great idea, I just don't think the 7-08 is the right case.
 

g0rd0

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I beilve that once you go to a longer case in the 08 class you end up with 3006 / 270 wich is too long. stick with neck siseing and your streaching problems will be corrected. But, if your head space is that far off try getting a NOGO gauge from Midwayusa or Brownell's if the nogo gauge will chamber in your rifle then it is time to bring it to a smith and have it corrected or if it is a new rifle contact the company to see what they will do for you
 
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Oct 6, 2012
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Thanks g0rd0, but what would give the best results then? Taking a 7-08 case and partially neck sizing it down or taking the 243 case and sizing it "up" with 7-08 die and then partially neck sizing it down?
 

royinidaho

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Thanks g0rd0, but what would give the best results then? Taking a 7-08 case and partially neck sizing it down or taking the 243 case and sizing it "up" with 7-08 die and then partially neck sizing it down?


The 7-08 partially necked down.

I don't know the most proper thickness but use the heavy back of a writing tablet to cut as a spacer under the ring of the sizing die.
 
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Oct 6, 2012
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The 7-08 partially necked down.

I don't know the most proper thickness but use the heavy back of a writing tablet to cut as a spacer under the ring of the sizing die.

Thanks for the advice and interest guys! Tried necking down and fire forming a 7-08 and it worked like a charm! Really appreciate it!:)
 

Brush4646

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Apr 30, 2003
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southwestern N.Y.
You don't have to go to 7mm08 brass just load the 243 bass with the bullets into the lands soas to hold the case against the bolt. Lube the case and shoot. Now back off your size die so you don't push the shoulder back again.
Brush
 
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Oct 6, 2012
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You don't have to go to 7mm08 brass just load the 243 bass with the bullets into the lands soas to hold the case against the bolt. Lube the case and shoot. Now back off your size die so you don't push the shoulder back again.
Brush

Thanks Brush, I'll try that!
 

bowhunthard

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You don't have to go to 7mm08 brass just load the 243 bass with the bullets into the lands soas to hold the case against the bolt. Lube the case and shoot. Now back off your size die so you don't push the shoulder back again.
Brush

+1 for this, it's what I was gonna recommend... Just seat the bullets far enough out to engage into the rifling so that it will keep the case head firmly against the bolt face. Just don't fireform with max loads, back it of a little, but don't use overly reduced loads either, as the fireforming would not be complete then.
 
Joined
Oct 6, 2012
Messages
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+1 for this, it's what I was gonna recommend... Just seat the bullets far enough out to engage into the rifling so that it will keep the case head firmly against the bolt face. Just don't fireform with max loads, back it of a little, but don't use overly reduced loads either, as the fireforming would not be complete then.

Thanks, tried it this afternoon and it works!:)
 

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