To weigh or not to weigh, that is the Question

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shooter64

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I never liked to weigh and sort my cases, so I was pleased to read Jerry Teo's views on the subject! But it did get me thinking.

If 2 cases have been prepped in exactly the same manner, and one weighs 1 grain more than the other, then it was assumed that this was caused by the wall on the heavier case being thicker (hence less internal volume), but exactly how much less? The answer is simply, the volume occupied by 1 grain of brass! Now I'm no mathematician, so please don't shoot me down, but I did some work last night using some online density calculators, and discovered the following,

1 cubic inch of brass weighs .303 pounds, so 1 cubic inch of brass also weighs 2121 grains........therefore 1 grain of brass is equal to .0005 cubic inches.

I measured some of my Varget powder (.03 diameter x .06 long) which has a volume of 0.0000424 cubic inches, so 0.0005 divided by 0.0000424 is approximately 12.

In other words, a case that weighs 1 grain more than another case, holds 12 particles of Varget less!

Perhaps someone with more intelligence could verify these results?
 
if you want to check the internal volume of your case, you need to weignt the water they can hold

just weight the brass is not acurate enough
just a little difference in the extractor groove, ou rim thicness will ruin the result

personally, I dont do it
but if I get a flyer, I mark the case and if next shot it gives me a flyer again, I take it out of the lot
 
shooter64 said:
I never liked to weigh and sort my cases, so I was pleased to read Jerry Teo's views on the subject! But it did get me thinking.

If 2 cases have been prepped in exactly the same manner, and one weighs 1 grain more than the other, then it was assumed that this was caused by the wall on the heavier case being thicker (hence less internal volume), but exactly how much less? The answer is simply, the volume occupied by 1 grain of brass! Now I'm no mathematician, so please don't shoot me down, but I did some work last night using some online density calculators, and discovered the following,

1 cubic inch of brass weighs .303 pounds, so 1 cubic inch of brass also weighs 2121 grains........therefore 1 grain of brass is equal to .0005 cubic inches.

I measured some of my Varget powder (.03 diameter x .06 long) which has a volume of 0.0000424 cubic inches, so 0.0005 divided by 0.0000424 is approximately 12.

In other words, a case that weighs 1 grain more than another case, holds 12 particles of Varget less!

Perhaps someone with more intelligence could verify these results?
Click to expand...


Also, if you would check your bullet/s, notice the variance. I've seen 1-2 grains at times. You will notice a bigger variance once you have finished a round.
 
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The proper way to sort your brass, check weight for one thats out by a lot and set aside.
Then load your ammo weighing powder with a good electronic powder measure app $300
.01 grains, fire all your ammo over good chrony all the ones are the same speed or very close 5 fps keep seprate they will be then called your match brass
 
I checked the math...it's good. However, the only way to measure a variance in internal volume is to fill the case with water and measure the mass of water. If your cases exhibit a 4 grain range, and you intend to group cases categorically by 1 grain variances, you would derive four "test" groups. For instance, Group 1=160 grain, Group 2= 162 grain, Group 3=163 grain and Group 4=164 grain in the instance of a typical .243 case weight. (all nominal wts.). You would need to use "rules" as well, for instance if a test cartridge weight was 160.5 grains, does it become a 161 gr nom Group 2 cartridge? I would think as such if you apply rounding rules.

Convert the mass of water back to volume by dividing the resultant mass of water that fills the case by the density of water (at the temperature you are measuring at - approx 1000mg/cm3). Then you arrive at variances in volume measurements between groups. Of course, then you may want to average results of a sample set of say 10 test cartridges. You may also wish to test your ability to reproduce the test result of a single cartridge to ensure that your method is repeatable.

At the end of the day, I have never done this, but it does make one think about internal volumes vs. variances in case weights and whether there may be a relationship. Or as above, the internal volume my not be overly affected by a variance in case weight, rather a anomally in the specific density of the brass between cartridges.

Good luck and post any results if you go for it!

I guess you could then convert the volume variance for cases that vary by 1 grain nominal, back to # particles.
 
I just did a sample of 15 cases tonight of case weight vs. water capacity. In my particular example with cases that varied from 180.2gn to 178.7gn the difference in water capacity was 0.1gn on average.

These were fireformed, and prepped cases, not new. So that MAY have played a roll???

Either way its a pretty quick test, try a few out. Weigh and mark cases, fill with water and weigh again. Simple.
 
You are talking about a ~64 mg in weight difference, which is 0.064 grams. The amount of gunk on the inside of the round would change the weight, if its rifle rounds and you trimmed the necks each one may not have lengthened more than another after being shot leading to variation.

And you say the water volume varied by "difference in water capacity was 0.1gn on average." Where if you check your scale it likely has a standard deviation of +/- 0.1 grain.

Hope this helps a little.
 
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