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Sorting Brass by weight

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Old 01-26-2012, 07:45 PM
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Location: Idaho Falls, Idaho
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Re: Sorting Brass by weight

My post was directed at sorting by case weight only. As Far as I understand it the dimentions of the chamber are the same regardless. of the capacity of the brass. After brass is prepped, trimmed and fireformed the brass then fits the chamber, making all of the variables from this point forward in the internal capacity of the case as long as neck length and neck thickness is consistant. This should, in theory, be where capacity from one case to the next differs. It should also be directly related to H20 capacity. As brass simply migrates, but doesn't dissapear it should remain the constant in the case. Therefore having a set volume determined by weight. I guess that diffrent brass alloys could have diffrent weights, but it would be pointless to go to that extent as that variable is so small as to be irrelivant.

I would point out that diffrent manufacturers do use diffrent thicknesses brass of same caliber/cartridges. For example, Hornady brass for the .270 Win is quite a bit thicker than Remington or Winchester. The brass was very consistant, but on average 20-24grns heavier than the other stuff. I found this out the hard way as after fireforming I loaded some border line loads for my 6.5-06 AI. They shot fine with Rem, Win, PMC and Federal Brass, I assumed (Which I have now learned not to do)would shoot fine with the hornady stuff. I blew 4 primers right in a row. The first 3 the primers fell out after I set the brass in the box (Still didn't pick up on it) the 4th locked up my action and then I realized that there was a big problem. My buddy was looking at the other brass when the primers fell out and we realized the capacity was less than the other brass.

H20 capacity is the only way to find true capacity, yet sorting by weight does serve it's purpose. Both are valid, yet I'm not to the point where I check by H20, I sort by weight now at least for this rifle.

Hope this clarifys my first post.

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Old 01-26-2012, 11:31 PM
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Join Date: Nov 2011
Location: central oregon
Posts: 225
Re: Sorting Brass by weight

mikecr if measuring by water is gonna drastically change the average shooters moa groups cool. lets see your tests and results. otherwords what you are talking about has no real world affect for the average guy. i am no benchrest shooter by no means but i have owned a rifle or two in many different calibers. most of which were able to shoot 1/2moa to 3/4moa with my little bit of knowledge.
i know thereis more than one way to skin a cat but we are talking on longrangehunting forum not 6mmbr. thats where you measuring with water might mean something.
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Old 01-27-2012, 10:46 AM
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Location: NC, oceanfront
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Re: Sorting Brass by weight

I'm not going to publish a paper on case sizing and capacity..
I've tested it, learned from it, it makes sense, easy to apply, and onward.

My contention here is that weighing brass is not the same as directly measuring case capacity. And I only bring this up for consideration w/resp to the topic.
I don't mean to imply that all shooters would benefit from capacity measure, or any other action beyond good case preps.
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Old 01-27-2012, 01:58 PM
B23 B23 is offline
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Location: Spokane, Wa.
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Re: Sorting Brass by weight

But does sorting by weight really have any correlation to case capacity???

I'm assuming the thought process is that a heavier case has less case capacity than say a lighter one because the heavier case is possibly thicker there for displacing internal case capacity but is this a common fact or are we just assuming the heavier or lighter case/s consistently has more or less case capacity???? If this isn't a common fact I don't see the point of weight sorting.

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Old 01-27-2012, 07:34 PM
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Re: Sorting Brass by weight

It MIGHT correlate,, or not.
The only way to know is to directly measure & compare weight -vs- capacity for a given cartridge and brass lot. And by this I mean every single case(not just a sample).
With this you'll know, and if it's important to you, then that's just what you'll do.

That velocity step changes from NEW brass to FIRE-FORMED brass, is observed enough with hunting cartridges to warrant consideration of capacity(IMO). Afterall, brass weight does not change with this, but capacity does.

I think brass weight is useful, as is thickness variance, and capacity. I do not think you should pick the easiest of these and rationalize that all is covered by that action alone.
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Old 01-27-2012, 09:28 PM
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Re: Sorting Brass by weight

Originally Posted by B23 View Post
But does sorting by weight really have any correlation to case capacity???
Yes. Here's why.

If you put a 1 cubic foot block of gold in a box that holds 4 cubic feet, there's only 3 cubic feet of volume left in the box. If the block of gold's only 0.9 cubic feet, there's 3.1 cubic feet still empty in the box.

The chamber has the same dimensions, and therefore volume, for every round fired. Cartridge brass is very homogenous; uniform in metal types distributed throughout it. So, the volume of the case brass itself, whether a cubic block of brass weighing 200 grains or a cartridge case of the same weight, is all the same. It subtracts from the chamber volume. And the case volume at peak pressure is what's inside the case with its walls pressed hard against the chamber. That's where it counts. And the case is pressed hard against the chamber wall when pressure in it is about 8000 psi; very early in the pressure curve.

Sort cases by weight, but only after they've been fired once then resized to their reloading dimensions. Otherwise, the small difference in actual new case interior volume may vary enough to cause a small difference in chamber pressure rise time and peak level.

A 1% spread in case weight's close enough. There's more variance in primer detonation flame levels and duration causing pressure and velocity changes than what all cases of exactly the same weight and volume will produce.
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Old 01-28-2012, 08:12 AM
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Posts: 2,114
Re: Sorting Brass by weight

While some may see a difference in accuracy or ballistic difference between new and fired cases that are sorted by weight, I've not. I get the same accuracy so any difference there is pretty darned small.
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