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Interesting brass reforming observation

jonk
I started out with 300 30-06 cases, USGI. 100 I left as 06. 100 I reformed and trimmed to 8mm Mauser, and 100 to 7mm Mauser.

The original 06 cases are still going strong, with about 5 lost due to neck cracks. The 8mm cases are by and large doing well, and have been reloaded a lot (10-15 times per case, with full length sizing, used in multiple guns) with maybe 10 lost due to neck failure.

The 7mm cases however, have suffered a 25% attrition rate within perhaps 5 loadings. A chamber cast of the one lone 7mm I have shows the chamber is not grossly oversized, so the brass isn't being overworked more than normal.

It would appear, then, from this experiment, that with regards to stress on brass, age and work hardening, and neck cracks, it is less stressful to open up a case neck than to squeeze it down.

Anyone else noticed this or just coincidence?
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Comments

7 comments

Date Votes
  • MIKE WISKEY
    "Anyone else noticed this or just coincidence?"...........did you anneal the cases before/after forming? reduceing the 06 body down to 7mm is a lot of 'working' (to 8mm not so much).
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  • Tailgunner1954
    Did you anneal the 7mm brass? I suspect this is the root of your issue.
    As your neck is now where the shoulder used to be, did you check for excessive thickness?

    Expanding thins the brass, reducing the diameter thickens it
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  • jonk
    As it chambered without neck turning, I didn't bother.

    I did not anneal. I find annealing overrated. It is an excellent tool IF done properly, but to do so properly, one really needs something to ensure each neck is heated uniformly and evenly. Otherwise, my results with the traditional 'torch in a pan of water' method have been that while it stops neck cracks, non-uniform results lead to a loss in accuracy.

    As I have something on the order of 5000 military 30-06 cases, I'd rather just lose them to attrition than bother with annealing. For more rare/expensive cases I do do it though.
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  • Rocky Raab
    Jonk, I am also a doubter of annealing - especially the ways it is currently done, most of which either don't actually anneal or ruin the cases.

    But hardened brass does sound like the culprit here. I'm purely guessing but I'd agree that thickening the walls (via necking down) might induce more metal fatigue than thinning them.
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  • JustC
    annealing is NOT rocket science. Use the correct Tempilac pen and you are good. Annealing is a NECESSARY operation for preserving brass life.

    If you are cutting down and reforming 06 brass to 7x57, you NEED to anneal properly before the operation.

    Don't forget, brass hardens with age, even if never fired or resized.
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  • mbsams
    quote:Originally posted by jonk
    As it chambered without neck turning, I didn't bother.

    The test for neck thinkness is to see if a bullet freely enters the case neck after firing. Just chambering isn't enough, lack of clearance to release the bullet and resultant high pressure is still possible.
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  • jonk
    quote:Originally posted by mbsams
    quote:Originally posted by jonk
    As it chambered without neck turning, I didn't bother.

    The test for neck thinkness is to see if a bullet freely enters the case neck after firing. Just chambering isn't enough, lack of clearance to release the bullet and resultant high pressure is still possible.
    It took me a few minutes of pondering to figure why that might be so, but makes sense. In any case, it isn't an issue anyhow, or I would have noticed pressure signs by now.
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