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Weight sorting brass

 
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  #8  
Old 07-09-2012, 05:43 PM
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Re: Weight sorting brass

I'm in the 'sorting out cases by dry weight is a bad move' camp.
There is no direct relationship between dry case weight and capacity.
You probably don't want to discard brass that matches the bulk in capacity just because it's dry weight is different, or to keep brass that departs in capacity even though it's weight is consistent with the bulk. Right?
You want your brass to match in capacity, right?
Then, measure that.

I sort fully fireformed/unsized cases by H20 capacity, and yes you can see a difference across a good chronograph and on target from this. The difference is predicted very well with Quickload also. The affect is exactly the same as any variation in load density.
I currently do this for 6br, 6xc, and 6.5wssm.

While Larger magnum cases present more volume to vary(regardless of case weight), they have a much wider pressure peak(the part affected by initial containment).
Small underbore cartridges(like a 6ppc, or 30br) can work around capacity variances through sheer extreme pressure loads.
Both of which put affects to peak pressure, and barrel timing -from capacity variance, in smaller percentage.
But mid-size cartridges(like mine) can't work around capacity variances, and I believe they are affected most by it.
That's why I check it.

You may be in a good position to check it nddodd, and you don't have to go through a lot of trouble to see if it's a worthy endeavor.
At the range with your normal load, point a chambered round straight up & carefully lower it to rest. But don't take so long as to allow the round to heat up in the chamber more than others.
If it's fired POI step changes away from the pack, then your load will be affected by capacity variances.
If not, I wouldn't bother sorting it at all.

I don't shoot any large magnums so I can't predict your result.
My 223s don't change with this test, so I don't sort them by capacity.
The others do -big time.
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  #9  
Old 07-10-2012, 06:59 AM
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Re: Weight sorting brass

Quote:
Originally Posted by Mikecr View Post
There is no direct relationship between dry case weight and capacity.
Except that if you feel the capacity of the case is only meaningful when the outside of the case is pressed hard against the chamber at peak pressure. That's when the outside dimensions of all the fired cases are exactly the same. Then the volume of the case equals the volume of the chamber minus the volume of the cartridge brass.

So, I weight cases to a 1% weight spread. This method may well cause the first part of the pressure curve to vary its shape more than weighing the water a case holds. It may also cause a small difference in muzzle velocity. I don't measure either one as I've no interest in either one. I don't know if anybody's accurately measured bullet drop differences at long range caused by both weighed cases and weighed water in cases that gets the same results within 1/2 inch for each test round fired. My cases sorted by weight do well enough to shoot long range groups equal to what benchrest record-holding ammo does.
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  #10  
Old 07-10-2012, 08:04 AM
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Re: Weight sorting brass

Thanks for everyone's input on this subject it is greatly appreciated. Mikecr I'll give your advice a try, thanks again guys.



Nathan
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  #11  
Old 07-10-2012, 08:38 AM
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Re: Weight sorting brass

Quote:
Originally Posted by Mikecr View Post
[...]
At the range with your normal load, point a chambered round straight up & carefully lower it to rest. But don't take so long as to allow the round to heat up in the chamber more than others.
If it's fired POI step changes away from the pack, then your load will be affected by capacity variances.
[...]
I was hoping someone else would ask so I wouldn't look stupid.
But, what are you measuring/testing here?
How does this relate to the significance of case capacity variability?
Would the results be different using a load with 90% fill vs compressed?

thanks!
Richard
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  #12  
Old 07-10-2012, 10:21 AM
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Re: Weight sorting brass

It shows that things significant to the outcome are happening BEFORE brass is mashed to chamber walls. You could dent your brass in and fire it to see similar. Same brass weight, same chamber.
You can change velocity with dies, and unsized new brass velocity will usually be higher than fireformed brass(sized or not), even though brass weight hasn't changed.
These things are causing INITIAL confinement & load density changes, and they do affect MV and barrel timing for many, even though the same brass will eventually expand to the same chamber.
That weighed FL sized brass shoots well enough, does not mean specific things can be generalized, just to make it so. There are too many contributors to do this.

The test I proposed affects only relative load density, and would not cause change with a compressed load. --I should have qualified that--
I believe it indicates whether a combination would be significantly influenced by load density variances, or not.
As implied, many combinations could be immune to this, while others are sensitive to it. I've tested what I shoot, and not a full gamut of combinations by any means.

As far as same brass weight mashing to same chamber volume, I don't believe that is happening. Magnum cases especially provide for weight variance -that does not contribute to capacity, regardless of chamber(like the belt and large rim & extraction groove).
But I think(a theory) that it may not even matter with magnums, considering their broad pressure curve.

Mid-size cases, even running faster powder, still take a bit of time to fully fit a chamber with any clearances. Any amount of time variance, confinement variance, influences powder burn rate and the pressure peak. These cartridges still do not burn all the powder in a barrel anyway, so pressure peak timing is very significant to outcome as less likely normalized further down the bores.

Underbore cartridges really shine with very high pressures. Not so much otherwise.
This works great, they completely burn up very fast powders even faster due to pressure. A glitch in their pressure curve due to initial confinement, or pretty much anything else, is insignificant as they're running flat against a wall of diminished returns anyway.
The great work-around.
This approach is viable with powder availability & capacity that provides for it, -with enough barrel steel around the chambers.
So far max capacity for this seems to be with the 6.5x47L, but time will really tell.
Larger diameter tennons will be needed to go further up with this to to 28 or 30cal.
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  #13  
Old 07-10-2012, 12:23 PM
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Re: Weight sorting brass

Mike - Thanks.

Plenty to think about.

Is Quickload much help as a learning tool in terms of modelling some of these effects?

The demo is pretty lame and the fact that you have to wait for someone to mail a CD gives me the impression (right or wrong) that it's not nearly as high tech as they'd have you believe.

-- richard
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  #14  
Old 07-10-2012, 03:01 PM
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Re: Weight sorting brass

QL is incredible. You play with it, calibrate for your/other loads, and run all sorts of 'what-ifs'.
I was an early adopter with my first version(maybe a beta) on floppy.
NECO is mom & pop-ish, but very reliable. I just upgraded again, and so far it's been worth it to do so now & then.
I use QuickLoad, QuickDesign, and QuickTarget which are integrated and export to each other.

Keep in mind there is NOTHING else that competes with QL. It is completely unique.
And you won't regret sending off for it.
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