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Severely Dented Cases….Secondary Explosion Effect?

 
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  #8  
Old 09-17-2013, 06:07 PM
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Re: Severely Dented Cases….Secondary Explosion Effect?

Seen this before
What caused my case to do this? (Help)

I don't know the answer. It would seem to me any pressure outside the case would not be greater than the pressure inside the case, regardless of chamber sealing. So I don't buy the low pressure load cause. But again, I don't know the answer.
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  #9  
Old 09-17-2013, 07:11 PM
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Re: Severely Dented Cases….Secondary Explosion Effect?

According to the Nolser book, my load of 88.4 grains of RL-25 is in the middle of thd powder range though.....showing 96% capacity. The light load theory makes sense to me but just not with my load.

For an update:
I loaded the exact same setup in a new case from a separate batch. I didn't size the new case either. (I did run the previous cases that were dented through my sizer) The thought being the new brass is already smaller than once fired brass so bumping the shoulder helped create the issue.

Results:
1.) same load in new unsized brass from different batch= no dent
2.) same load with the original new unsized brass= no dent
3.) new brass ran through my sizer with 92gr retumbo= no dent.

All in all, I think sizing the new brass was a mistake on my behalf and maybe a bad batch of brass.
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  #10  
Old 09-18-2013, 02:01 AM
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Re: Severely Dented Cases….Secondary Explosion Effect?

I've read that it is from too light of powder charge developing not enough pressure. I have a 7 rum. Keeping my loads towards the upper spectrum has resulted in this not ever being an issue for me. Right now I run a 140ab, rem case, 90.6 gr 7828, rem 9.5M primer and the load gives me 3400 fps @ 15ft as chrony'ed. While the charge wt of 7828 may be over max for the manuals, the velocity out of the 26" bbl is by no means out of line. I have run it up to over 3500 with rl25 and retumbo both. RL25 is slower than 7828 and your only at 88 gr so I would guess that its a fairly mild load. Now that doesn't explain all the variables you've mentioned but I would reason that running hotter loads will keep you from experiencing this phenomenon.
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  #11  
Old 09-18-2013, 02:12 AM
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Re: Severely Dented Cases….Secondary Explosion Effect?

And my guess as to how dented cases happen in the 7 rum; a mild load that does not develop pressure fast enough to seal the neck to the chamber but does develop enough to seal the case body to the chamber. The gas that has sneaked back past the neck collapses the shoulder of the case. and as you have stated there are many contributing variables such as brass hardness, etc that can help contribute to this happening. When the conditions are right-it happens. JMHO but its just a wild assed guess mostly.
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  #12  
Old 09-18-2013, 06:13 AM
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Re: Severely Dented Cases….Secondary Explosion Effect?

Now see on my burn rate chart it shows RL-25 and imr 7828 being on the same level for burn rate and then Retumbo being one step slower then the two of them.

In both my 300 rums and in my 375 rum i run them on the hot side of the Scale. And in my semi custom 300 rum I run it over max for best performance. I also run them .020" off the lands and single feed in ever single rifle I have. But I have never had this problem.

I'm confused on what not sizing the case did for you when you used it as a variable??

I think alot of people have problems with the rum calibers because they are under loading them in hopes to have a longer barrel life... Rums were ment to push hard and fast, if a guy wants barrel life buy a standard magnum. 7mm rem mag, 300 win mag etc..

Just my two cents hope you get you problems worked out. Good luck sir.
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  #13  
Old 09-18-2013, 05:40 PM
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Re: Severely Dented Cases….Secondary Explosion Effect?

I see it as a puzzle, and would love to learn the actual cause.

The cases seem not merely failing to fully expand at a local area. They're seem formed INWARD there.
And, there is no discoloration within the form. The sooting stops at the necks/shoulders.
I can think of nothing that would cause external to case pressure greater than internal case pressure.
If it were a pocket of powder late igniting there would be discoloration from it.
Any interference with full expansion would just cause that, and not inward formations.
The inward formation is what throws me.

Is it really inward, or was the brass sized so much under chamber that it's really a local failure to expand?
I don't see any SINGLE possibility as a cause, but some rare combination of factors.
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  #14  
Old 09-18-2013, 07:43 PM
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Re: Severely Dented Cases….Secondary Explosion Effect?

DAMN! I would check other books also. this does look like a low pressure load.
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