223 testing results

[Metal god]

I thought the idea of sorting brass by weight has been proven to mean nothing or was it weight has nothing to do with volume? I guess I’ll need to go look at my weight and volume data an see what it actually says . Actually I believe I’ve posted that data here in at least one thread , maybe I’ll be able to find that rather then reposting everything again .

 

[tangolima]

I think first you need to sort by head stamp to make sure close match of material. Brass density variation affects powder capacity more significantly than weight. Then brass with identical head stamp are to be sorted by weight.

Brass density has range of +/-4%. Head stamp sorting cuts it down, to say +/-2%. The corresponding powder capacity variation is +/-0.7% for .223 Rem. I would like to weight sort the brass with matched head stamp to have significantly lower effect on powder capacity, say +/-0.1%. The weight sort range is 0.8%, or +/- 0.75gr for .223. I do +/-0.5gr.

This is based on equations I have derived for .223. It is different for different calibers.

-TL

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[Unclenick]

Percentage variation in brass weight is not the same as the percentage variation of powder capacity.

That is correct, but my point was the difference in brass weight is also not reliably proportional to the difference in powder capacity. The head tolerances alone can cause several grains of weight variation before you even get to the part of the case that holds the powder.

What I did, specifically, was resize and trim mixed headstamp 308 cases. I then weighed the cases and divided the case weight differences by the specific gravity of cartridge brass (see ρb values below based on this alloy analysis) to try to predict the difference in space made (or taken away) for case water overflow capacity. I then plugged the primer pockets, re-weighed the cases, and then filled them with outgassed water (to prevent bubbles) level with the case mouths (no meniscus), weighed them again, and subtracted the unfilled weight to learn how much water weight they were holding in grains. What I found was that if the difference in brass weight predicted a 1-grain difference in water capacity, the measured difference in water capacity might be anywhere from 0.8 grains to 1.2 grains. In other words, ±20% prediction accuracy is based on the difference in brass weight alone.


Added information for anyone who cares:

LC, ρb=8.53 g/cc
Win,ρb=8.56 g/cc
Lapua, ρb=8.60 g/cc
Norma, ρb=8.63 g/cc
Federal,ρb=8.64 g/cc
Rem, ρb=8.69 g/cc

 

[tangolima]

Thanks for sharing the density data, unclenick. The variation among those manufacturers is about 2%, which is about half of what I have assumed. Head stamp sorting should reduce it much further.

I see your point on the error term due to variations in the dimensions around the extraction groove. I'm updating my derivations to include it. With powder capacity versus brass weight data points, that error term can be extracted and accounted for.

In the meantime, even with the 20% error, weight sort should still work. We just need to tighten the acceptance window.

Say for .308 win, nominal power capacity is 56gr H2O. If I want to limit the variation to 1%, or 0.56gr, I tighten it to 0.47gr to account for the 20% error. That translates to about 3.7gr acceptance window in brass weight sorting.

So far I found stamp sorting is most critical for .223 rem, which has smaller powder capacity of 32gr H2O. The acceptance window for brass weight sorting is 0.75 - 1gr, and I have to ditch about 50% of the brass I bummed from the range to meet that goal.

-TL

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[44 AMP]

I thought the idea of sorting brass by weight has been proven to mean nothing or was it weight has nothing to do with volume?

Not "nothing" but not "absolutes", either.

Consider this, since the brass is the same size on the outside, and capacity is determined by the size of the inside, the heavier case must have either thicker walls (more brass) OR it has the same thickness walls made up of a heavier alloy.

SO, the heavier brass MAY have less capacity, OR it may have the same capacity and be made of a more dense alloy.

There is a relationship, but its not an automatic one where every batch of cases from every maker can be plugged into a general formula and have accurate results.

I think this is one of those things where formula can predict general trends but actual differences (amounts) must be determined by weighing and measuring the cases you are working with.

Or not bothering to worry about it, and just working up your loads with what you have, specific to what you have.

for example, GI brass is usually heavier than some/most commercial brass, but you can't tell exactly how much of a difference that is going to make only that there will be a difference, the exact amount of which requires measuring what you have.

 

[tangolima]

I have never paid much attention to head stamp and weight sortings till recently, when prices for everything has elevated. Making everything round count is way to conserve.

-TL

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[jetinteriorguy]

I used to obsess over this stuff but finally quit driving myself crazy over it. All I ever proved was that no matter what I did, with my ability and equipment I’m a solid 1/2-1 MOA shooter. But, I did prove to myself that with good ammo and the right load I’m happy with that. This is pretty easily achieved with good diligent methods but not so totally perfect loading technique.

 

[zeke]

Once did a test with about 6 varieties of 308 brass with the same powder charge, primer firearm. With a lower than max load, the heavier cases consistently gave a slightly higher velocity, and almost a direct correlation between weight and velocity difference. Albeit the rounds per case were limited. Fed brass was the heaviest commercial brass weighed (close to milsurp), and Win the lightest. The main point being to consider what brass was used in load manuals when working up a load.

And am always wondurus about the capability to accurately measure the weight/volume of water in a case. Certainly the density of brass may matter, but given the amount of brass in the cases involved, gotta wonder how much it matters.

 

[Unclenick]

You can see from the numbers I gave that the range is about 2% density difference. 308 Win cases are in the 55-60 grain water overflow capacity range. Out of that, the alloy can be responsible for up to about 1 grain of capacity difference. So, while I gathered that data off of Matweb, I still think the head tolerances are the big noise.

Here's an illustration of the SAAMI minimum dimension and maximum dimension case head:

 

[tangolima]

Unclenick. Because brass is much denser than water, it takes about 8gr of brass to make one grain of water. I don't know the average weight of .308 brass, say 150gr. 2% is 3gr or less than 0.5gr water equivalent. That's what I meant the percentage variation in brass weight cannot be directly translated in powder capacity.

-TL

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[Metal god]

308 brass is 170 to 190 grains . All my LC brass is in 180 to 185 area . I have some Remington thats in the the low 170’s and heard of old Win brass being as light as the 150’s .

I said I was going to have to look at my data . Haven’t yet and out of town now . “If” I remember when I get back I’ll post the case weight to volume data I have .

 

[tangolima]

Metal. It would be wonderful if you can post your data. I have updated my equations to include the external dimension error. But I need real measurement data points.

Just picked up 50 or so Norma .223 brass. They seemed to be from the same batch. Did a weight sort. They are absolutely the best I have seen, even better than RWS. All 50 pieces neatly sit between 91.5 - 93.3gr. Amazing!

-TL

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[Unclenick]

Here's data from a brief weighing of Lapua brass. The histogram quite clearly reveals two sets of tooling were involved. If I had doubled the sample size, you would have seen the bell curve shapes of each tool's product's weight distribution much more clearly.

The Winchester .308 cases made for the 1992 Palma Match, which the U.S. hosted, weighed a scant 150 grains, IIRC, having been redesigned for maximum powder capacity, which was accomplished in part by going to the semi-balloon head design, which they seem to have migrated to other cases (it saves brass cost). In 2001-2005 somewhere, I bought 500 pieces of Winchester new brass on Commercial Row at Camp Perry and weighed them all. The distribution is in the illustration below. You can see four distinct tooling sets were involved, each making its own bell curve peak. The tails overlap, making it impossible to sort by tooling exactly. I note that a few more recently purchased Winchester cases were in the 162-166 grain weight range, probably reflecting changes after the 2007 shift of centerfire ammunition manufacturing from East Alton, IL, to Oxford, MS.

 

[akinswi]

Nick,

Is there any correlation to brass weight vs volume?

When I went to shooting 1 manufacturers brass on a lot to lot basis, I did get better scores, I dont shoot many groups anymore Just scores

I found weighing brass and bullets got to be too tedious for my liking. But the graph is very interesting .

 

[Unclenick]

All that Winchester brass came in the same bag, yet clearly was off four different machines. One time I measured a number of 308 cases by weight, then I divided the weight difference by the density of 70:30 brass to get a change in water weight for the same volume change, then did actual water capacity measurements of them, and I found the water capacity change was predicted by the weight difference to an accuracy of ±20%. So some of the weight difference (this was mixed brass) was due to head tolerances down below the bottom of the powder space. I have been trying to find what I did with the original record of that, but may have to repeat it. Also, this kind of thing can change over time as manufacturers contract out to each other or tooling changes.

 

[std7mag]

While interesting data, (Thank You for the time & effort spent to the OP!!), unless your shooting an AR with bulk FMJ it really means little.
At least to me.

Had you been testing with a free recoiling benchrest rifle using match bullets (along with a trigger set in ounces, not pounds) and slow fired.
That might have proven whatever concept you were looking to achieve.