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cases streatching - headspace?

 
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  #8  
Old 08-16-2013, 09:22 PM
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Join Date: Jul 2013
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Re: cases streatching - headspace?

My SAAMI length is 55.12. I measure and trim cases after resizing. And I hade many cases upwards of > 55.4

That seems a lot in my mind.
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  #9  
Old 08-17-2013, 09:06 PM
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Location: NC, oceanfront
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Re: cases streatching - headspace?

You guys are squeezing the brass up like toothpaste, and trimming it away to change your case capacities, and create donuts and runout.
The results of choices you make..
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  #10  
Old 08-18-2013, 09:28 AM
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Re: cases streatching - headspace?

Quote:
Originally Posted by Mikecr View Post
You guys are squeezing the brass up like toothpaste, and trimming it away to change your case capacities, and create donuts and runout.
The results of choices you make..
Mike, while this might be one of your favorite axes to grind, for the benefit of all the others who do, here's some realities regarding it.

Many top ranked rifle shooters winning matches and setting records have been doing this very same thing for decades. When done in moderation, the benefits far out weigh an insignificant change in case capacity (after 5 cycles, it may require a 1/18th MOA correction on the sight) but it's never been a concern as far as runout becoming an issue. Such practices have produced test groups in their rifles smaller than current benchrest records.

The folks who do it the most are those few who full length resize fired cases testing match bullets for accuracy at Sierra Bullets' plant in Missouri. The best of those HPMK pills shoot into 1/4 MOA in their 200-yard test range.

While you may regurgitate from mental nausea at the thought of doing what other successful folks have done, that's fine by all of us who do. Take a deep breath, relax and be sure you've enough paper towels and tissues to clean up the mess you make.

Exactly how much case capacity is changed by removing a cartridge brass tube .335" diameter, .010" long with a .013" wall thickness thats removed form a 30 caliber cartridge case that weighs 200 grains? How much of a change in point of impact will that make?
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  #11  
Old 08-18-2013, 02:17 PM
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Location: NC, oceanfront
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Re: cases streatching - headspace?

Other than point blank BR I suppose, not all competitive/record holding BR shooters FL size.
At least not in LR BR. Not all anneal every reloading either. That notion out there is just completely fabricated. Truly there is nothing that ALL do.
The way I see it, the basis that 'everyone is doing it' is not born of reasoning, and therefore unlikely to change as a result of reasoning.

For those who are content with their FL sizing, I'm glad for them. I know there are situations where FL sizing is appropriate, and I'm not out to convert them.
But many many issues, directly resulting from FL sizing and continually puked across shooting forums, are merely the result of choices.
This is where I go with it. To inform folks that they are not locked into these issues, despite advice elsewhere. They can plan, make choices, and stop chasing their tails.

You and I don't agree, and you have your messages and I mine. It makes for good contrast in discussion and I don't wish to ruin threads with personal attacks. Let's not.
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  #12  
Old 08-19-2013, 08:57 PM
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Location: Mountians of SW NC, near Asheville
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Re: cases streatching - headspace?

You set the shoulder back .0015" from fired position? You know that fired position is at least a thou less than the chamber length? The firing pin will drive most bottle neck cases forward another thou and then the exploding primer will do almost that much more? End result would then be close to 1.5 + 1 + 1 = 3.5 thou shoulder set back with ignition which will require almost that much stretching when fired again. If you're gonna shoulder bump every time you will likely get pretty much that result every time.
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  #13  
Old 08-19-2013, 09:06 PM
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Join Date: Jan 2009
Posts: 451
Re: cases streatching - headspace?

Quote:
Originally Posted by boomtube View Post
You set the shoulder back .0015" from fired position? You know that fired position is at least a thou less than the chamber length? The firing pin will drive most bottle neck cases forward another thou and then the exploding primer will do almost that much more? End result would then be close to 1.5 + 1 + 1 = 3.5 thou shoulder set back with ignition which will require almost that much stretching when fired again. If you're gonna shoulder bump every time you will likely get pretty much that result every time.
What is your suggestion. I'm not here to get in a piszing match, I'm trying to learn.
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  #14  
Old 08-19-2013, 09:32 PM
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Re: cases streatching - headspace?

Quote:
Originally Posted by boomtube View Post
The firing pin will drive most bottle neck cases forward another thou and then the exploding primer will do almost that much more
I agree the firing pin drives the case forward until its shoulder stops against the chamber headspace point; chamber shoulder for rimless cases, rim or belt shoulder in the chamber for these.

I've fired dozens of live and dead primed empty rifle cases as well as near two dozen live and a dozen or more dead primed and bulleted rifle cases without powder in them. None of them had any evidence of the primer alone drive those bottleneck cases forward. Shoulder setback was the same across all of them. Those with bullets seated did not move the bullet at all from the live primer firing. And all the primers remained flush with the case head as they were when first primed.
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