Brass weight variance

[jsthntn247]

I sorted some 223 Lapua brass last night and weights ranged from 93.7 to 97.8 over 200 pieces. Are most of yall seeing this much variance in your brass?

 

[savagedasher]

Its not the case weight that matters it is internal volume. Larry

 

[Ledd Slinger]

+1 on case volume.

But when weight sorting, you need to put your data in groups, numbers, and perhaps even percentages. All brass will have some oddballs. That's the whole reason for weight sorting. Did you have 90% of the brass around 95gr and a few low and high oddballs? Or was there 30% 93.7gr, 30% 96 gr, 30% 97gr, 10% 97.8gr? See what I'm asking? If you just had a handful pieces that threw the spread off, no big deal, but if 95% or more of the brass was in 1 to 2 grains of each other, i would say that's good.

Just not enough detailed info to say if you have a batch of brass that is out of spec.

 

[jsthntn247]

I had 8 pieces in the 93.7-93.9 range. 29 pieces from 94-94.4 32 from 94.4 to 94.8 40 from 94.9-95.4 45 from 95.4 to 95.9 40 from 95.9 to 96.5 and 6 above 97. I ended up putting into two batches to be used seperately 94-94.9 and 94.9-96.5.

 

[Ledd Slinger]

So you had 186 cases within 2.5gr of each other and only 14 cases out of that range. Then you work from the outsides in til you get you get what you consider an acceptable variance. By the time you get most of your highs and lows sorted out from the middle range of a 2.5gr spread, you may find that you only have 20 cases that don't meet a weight range spread of 1 to 2 grains.

There's nothing wrong with heavy or light cases. You have to have foulers, dummy rounds and brass for barrel break-in procedures. That's what I use those brass for.

 

[jsthntn247]

I understand what you mean. My last batch of Norma had a spread of 1.4 grains over 350 pieces. Just figured lapua would have been better or at least as good as the Norma.

 

[Ledd Slinger]

I understand what you mean. My last batch of Norma had a spread of 1.4 grains over 350 pieces. Just figured lapua would have been better or at least as good as the Norma.

Well like the previous poster stated, case volume is the most important thing. I bet if you measure case capacity with water on every piece, the Lapua would out perform the Norma. But that's just an assumption...You could have a whacky lot of brass.

 

[jsthntn247]

I'll just have to shoot it and see if I have vertical issues then measure the pieces that go high or low.

 

[jimcasey01]

http://forum.accurateshooter.com/index.php?topic=3858943.45

Dry weights to water capacity on .223 rem brass, Lapua, a few months ago. Most of my weights are in grams, but I converted the weights to grains.

 

[Ledd Slinger]

http://forum.accurateshooter.com/index.php?topic=3858943.45

Dry weights to water capacity on .223 rem brass, Lapua, a few months ago. Most of my weights are in grams, but I converted the weights to grains.

Nicely done. Now that's how you do it if ultimate accuracy is your goal

 

[Ackman]

I sorted some 223 Lapua brass last night and weights ranged from 93.7 to 97.8 over 200 pieces. Are most of yall seeing this much variance in your brass?

Don't worry about it. You're sorting caseweights with the purpose of getting consistent internal volume and it doesn't work that way. Caseweight isn't an indicator of more/less internal volume. Sorting into groups won't accomplish what you want.
Several years ago I wanted to find out if more weight means less volume. It doesn't. It's easy to check. Go through cases and pick the heaviest, and the lightest, and a range in between. I did this with Winchester and IMI .223 brass. (IMI is very good match grade stuff, there's a reason for this). Cases were all fired, then trimmed to the same length.

Caseweight......IMI had about the same variation as your Lapua and about 3x as much variation as Winchester.

Water Volume.....IMI had only about 1/2 the internal water volume variation of Winchester.

Volume to weight.....IMI - the heaviest case also held the most water. Lightest case was somewhere in the middle with water volume. Winchester - the lightest and a mid weight case both held about the most water. The heaviest did not hold the least.

I've not done this with other cartridges, but sorting .223 by caseweight is meaningless. Worrying about weight groups and percentages is self delusion. Next time neckturning or trimming, take a sliver of brass and weigh it. Doesn't take much to weigh a couple grains. Then imagine that small volume can be anywhere on the case. Think about the times loading 500 or more .223's and how they don't all fit the same in the shellholder...... and occasionally one just doesn't fit. Don't waste your time weighing and sorting.

 

[Ledd Slinger]

Great info Ackman. After reading this thread, I think I'll put less concern on weight sorting in the future as well.

 

[lpreddick]

i weight sort new brass into 2 or 3 batches more to be sure to rotate them when shooting. bag A first, bag B next, etc. put the fired brass in their bag and put at the rear of the container...everybody gets shot the same number of times.

 

[CatShooter]

I sorted some 223 Lapua brass last night and weights ranged from 93.7 to 97.8 over 200 pieces. Are most of yall seeing this much variance in your brass?

Don't worry about it. You're sorting caseweights with the purpose of getting consistent internal volume and it doesn't work that way. Caseweight isn't an indicator of more/less internal volume. Sorting into groups won't accomplish what you want.

[...]

Good morning Ackman...

Here is some stuff to think about.

First, to get one red herring out of the conversation...

... Some guys say that the grove variations can affect weight - but I did volume/density of brass calculations, and found that a group of cases that have groove diameters that vary by 0.005" (which is a lot) - that the 0.005" variation is only responsible for 1/10th of a grain of weight (that one surprised me too). So we can remove extractor groove variation from the discussion.

OK. The volume of a case in a static state is NOT the same volume of the case under pressure, and it is only the volume under pressure that counts.
A good example is taking a 22-250 AI - the same load in new cases and in fire-formed cases (same box of cases), is the ~same - I have found this, and you have found this (you have spoken of it often)... because the case fills out the chamber almost instantly in the firing cycle. So it is not the volume of the static case that we are interested in, it is the volume when the powder is burning and the bullet is being pushed by the pressure created by that volume.

If we consider the things that can affect case/chamber volume, the only thing is the amount of brass - because the case will fill out the chamber to seal it so the only space left in the inside of the case.

But it is a mistake to think that if you put water in the case, that you are getting the volume of the case when it is working, because...

1 - variations in body hardness will mean variations in body spring back, which mean variations in water volume.

The only way to determine accurate water volume in a group of cases is to force the cases to be the same physical size.
That can only be done if they are in a small die that forces all the case bodies to conform to the same size - kinda like a chamber under pressure, but in the opposite direction.

I did this once by using a file-trim die, and filling cases with water, while the case was up in the die - then I filled it, leveled the water, withdrew it, and weighed it.
When I numbered the cases with a "Sharpie" pen, and fired and measured and fired and measured... the water in cases was repeatable.

But when I just put water in cases and weighed them, and repeated the above sequence, WITHOUT putting the cases in a constricting die, the water volume varied each time... because the cases do not spring back the same amount from the chamber walls each firing, they do not spring back "out" the same from each sizing, because the amount of anneal of bodies is not uniform, no matter who makes the cases.

Through out the whole process, you are dependent on the elasticity of the case walls to all spring back, and up, the same amount... which they do NOT!

So if you want to use water to measure case volume, you MUST constrain the body dimensions so all the cases are the case physical size, or your efforts are wasted.

When I used the File-trim die to constrain the cases, I found there was a direct and linear correlation between case weight and water volume... so, now, if I am being anal for my bench or LR rifles, I weigh the cases.

 

[joshb]

Wow Cat! Long explanation. And informative. Thanks for taking the time.

 

[savagedasher]

Case volume should be checked on new cases after the second reloading fired in the same gun. Remove the primer and install up side down, Trim the case to the exact length. Fill the case with water and dry the case. The problem is the bubble is any difference in shape gives a false reading. The brass from being new and fired in the same gun the spring back should be the same.
Its no different then CC cylinder heads. The move with pressure just like a case does. I have 4 cases that weigh the same and internal volume is 1.2 gr different. Larry

 

[jsthntn247]

How would weighing with water and 90% alcohol differ. Since the alcohol is lighter would you need to shrink your variance groups ie 1gr of alcohol difference is equal to x amount of water difference.

 

[Ledd Slinger]

Great info Catshooter. I'll have to test that out some time on my brass.

 

[ronemus]

I did an experiment several years ago to determine just how much effect brass weight has on .223 loads. I used WW brass (sized, trimmed and deburred, primer pockets uniformed, flash holes deburred, and neck turned) , WSR primers, charges of RL-15 or N-550 powder weighed to 0.1 gr, and 75 gr A-Max bullets. Using the lightest and heaviest cases (sorted from 1000 once-fired I had on hand), I had two lots of 10 cases with a 3 gr difference in weight. The average muzzle velocity difference was 16 fps, just a bit more than the 12 fps due to 0.1 gr of powder. I choose to sort 0.5 gr lots of .223 brass for my long range loads, but the effect will only matter at 800-1000 yards - the vertical displacement on the target from such a small velocity change is negligible at shorter distances. Unless you control all other sources of variation, the effect of brass weight is negligible. I also shoot .284, and because the brass is twice as heavy I batch in 1 gr lots.

 

[searcher]

I think Catshooter is on the mark. Good example