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For Those That Weigh Brass

 
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  #15  
Old 06-16-2011, 04:33 AM
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Re: For Those That Weigh Brass

I used to weigh and sort virgin Lapua and Norma brass, but the quality is so good, that I no longer waste the time. Rem, W-W and Fed vary considerably and should be weighed and culled.

When you remove small amounts by trimming and turning necks, it does change the weight somewhat. For that reason, I think that if you want to do this, it should be done out of the bag. I tried weighing volume with water also, but its a mess and too time consuming.

Of course, if it makes you feel good to weigh and sort brass, by all means do so.
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  #16  
Old 06-16-2011, 10:00 AM
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Re: For Those That Weigh Brass

Bart B
I think your theory about cases of same weight holding same capacity -once expanded to the chamber walls, is somewhat true(minus weight from brass that doesn’t expand to a chamber dimension).
Along with this, the chamber is part of a dynamic volume, ever increasing with bullet travel.
So you could argue(if your theory were true) that by the time a bullet travels 25” down a bore, the chamber itself is too small a percentage of total volume to matter much.
And still connecting your dots, since the bullet is released by neck expansion before it evens moves, and those necks always go to the same chamber dimension, then neck tension variance wouldn’t matter much.

But, the affects of initial containment(volume) apply way before then, and this holds as significant to ignition and the timing of it.
Weigh out and load a case half full of powder, no bullet. Chamber it pointed up and fire –WUMP…
Now do the same but with a fold of tissue setting on the powder –BOOM.
This night & day difference was not expanded volume of the case to chamber, or a difference in powder amount. It was a change to INITIAL containment, which affects ignition timing right from the git-go.
Neck tension changes ignition because it varies containment/ignition timing(like the tissue), and so the pressure peak, and area applied.
Same with case volume, and fill density.

This can be seen across a chronograph, and shooters notice higher velocities from first firing of new brass, over second firing of it.
Yes this brass all went to nearly same capacity with it’s first firing. But not before affecting ignition.
Wouldn’t you agree?
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  #17  
Old 06-16-2011, 11:31 AM
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Re: For Those That Weigh Brass

Quote:
Originally Posted by Mikecr View Post
Bart B
I think your theory about cases of same weight holding same capacity -once expanded to the chamber walls, is somewhat true(minus weight from brass that doesn’t expand to a chamber dimension).
I think it's exactly true. Especially if you discount the case head which doesn't expand any significant amount up to almost where the pressure ring is.

Quote:
Along with this, the chamber is part of a dynamic volume, ever increasing with bullet travel.
Yes, that's the way it is.

Quote:
So you could argue(if your theory were true) that by the time a bullet travels 25” down a bore, the chamber itself is too small a percentage of total volume to matter much.
I'm working on a spreadsheet to calculate chamber and case volume. Rough estimate for a 26-inch long 7mm Rem. Mag barrel shows the case volume is about 20% of the bore volume. A 1:5 ratio's quite a bit.

Quote:
And still connecting your dots, since the bullet is released by neck expansion before it evens moves, and those necks always go to the same chamber dimension, then neck tension variance wouldn’t matter much.
I don't think so. The bullet gets pushed out of the neck and the case neck expands behind it. There's no force on the inside of the case neck where it touches the bullet. Virtually all the force is against the base of the bullet which pushes it out of the case neck then into the rifling. Once the bullet heel's clear of the case mouth, then the whole neck's expanded all the way out to the chamber's neck wall.

Quote:
But, the affects of initial containment(volume) apply way before then, and this holds as significant to ignition and the timing of it. Weigh out and load a case half full of powder, no bullet. Chamber it pointed up and fire –WUMP… Now do the same but with a fold of tissue setting on the powder –BOOM. This night & day difference was not expanded volume of the case to chamber, or a difference in powder amount. It was a change to INITIAL containment, which affects ignition timing right from the git-go.
What about the case with tissue stuffed in between powder and bullet? This puts near twice as much powder closer to the flash hole. More powder gets ignited in those first few microseconds than a case half full of powder where half the powder's in the front half of the case body.
Quote:
Neck tension changes ignition because it varies containment/ignition timing(like the tissue), and so the pressure peak, and area applied.
Same with case volume, and fill density.
Again, right on these, too.

Quote:
This can be seen across a chronograph, and shooters notice higher velocities from first firing of new brass, over second firing of it. Yes this brass all went to nearly same capacity with it’s first firing. But not before affecting ignition. Wouldn’t you agree?
Probably with neck only sized cases. With my full length sized ones there's no noticable difference in the chrony tests I did. Never tested the diffference using neck only sizing. With the same load producing the same peak pressure, they all will expand to a perfect fit in the chamber, all will have the same case volume. New cases will spring back more than fired cases. The more times a case gets neck sized, the larger its body is after each firing, both in headspace and diameter. Proper full length sized cases don't do that.

Last edited by Bart B; 06-16-2011 at 04:34 PM.
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  #18  
Old 06-19-2011, 02:07 PM
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Re: For Those That Weigh Brass

I am going to start weighing my brass as of now..... Thanks for the great thread..
Pete
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