Weight distirbution of Lapua .308 Brass

[repiv]

I have read on here about people weighing brass and sorting it. Up to now I have never done it myself but I thought hmmm I wonder (this is normally where trouble starts). So I did weigh my 100 pieces of .308 Lapua brass. What I came up with kinda surprised me. The left side is the weight and the right is the number of pieces of brass for each given weight.

174.6-- 1
174.5-- 0
174.6-- 11
174.5-- 10
174.4-- 8
174.3-- 8
174.2-- 7
174.1-- 7
174.0-- 4
173.9-- <span style="font-weight: bold"><span style="color: #FF0000">0</span></span>
173.8-- <span style="font-weight: bold"><span style="color: #FF0000">0</span></span>
173.7-- <span style="font-weight: bold"><span style="color: #FF0000">0</span></span>
173.6-- <span style="font-weight: bold"><span style="color: #FF0000">0</span></span>
173.5-- <span style="font-weight: bold"><span style="color: #FF0000">0</span></span>
173.4-- <span style="font-weight: bold"><span style="color: #FF0000">0</span></span>
173.3-- 2
173.2-- 3
173.1-- 7
173.0-- 9
172.9-- 11
172.8-- 7
172.7-- 2
172.6-- 3

Now for the record this brass has been fired 3 times and has not been trimmed in any way. Some of the heavier pieces are bit shorter than some of the lighter ones.
So my reason for posting this was not to come to some kind of conclusion about this data or to help formulate a plan of action as much as it was just to ask if anyone else is seeing this and is this normal? And if this is normal why does brass like Lapua have this variance. I would expect variations in the weight of any brass. But I would have thought there would be a more even distribution between 172.6 and 174.6 or at least a single spike somewehre in the middle. It seems that with my 100 peices there are heavy ones and there are light ones with none from 173.4 to 173.9. I thought this was a little strange.

So is this the norm or is this just this box of 100? Im not gonna lose sleep over it either way just curious.

I also came across this post
http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=1267476


edit for spelling, fixed link

 

[ChrisGarrett]

Re: Weight distirbution of Lapua .308 Brass

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: repiv</div><div class="ubbcode-body">I have read on here about people weighing brass and sorting it. Up to now I have never done it myself but I thought hmmm I wonder (this is normally where trouble starts). So I did weigh my 100 pieces of .308 Lapua brass. What I came up with kinda surprised me. The left side is the weight and the right is the number of pieces of brass for each given weight.

174.6-- 1
174.5-- 0
174.6-- 11
174.5-- 10
174.4-- 8
174.3-- 8
174.2-- 7
174.1-- 7
174.0-- 4
173.9-- <span style="font-weight: bold"><span style="color: #FF0000">0</span></span>
173.8-- <span style="font-weight: bold"><span style="color: #FF0000">0</span></span>
173.7-- <span style="font-weight: bold"><span style="color: #FF0000">0</span></span>
173.6-- <span style="font-weight: bold"><span style="color: #FF0000">0</span></span>
173.5-- <span style="font-weight: bold"><span style="color: #FF0000">0</span></span>
173.4-- <span style="font-weight: bold"><span style="color: #FF0000">0</span></span>
173.3-- 2
173.2-- 3
173.1-- 7
173.0-- 9
172.9-- 11
172.8-- 7
172.7-- 2
172.6-- 3

Now for the record this brass has been fired 3 times and has not been trimmed in any way. Some of the heavier pieces are bit shorter than some of the lighter ones.
So my reason for posting this was not to come to some kind of conclusion about this data or to help formulate a plan of action as much as it was just to ask if anyone else is seeing this and is this normal? And if this is normal why does brass like Lapua have this variance. I would expect variations in the weight of any brass. But I would have thought there would be a more even distribution between 172.6 and 174.6 or at least a single spike somewehre in the middle. It seems that with my 100 peices there are heavy ones and there are light ones with none from 173.4 to 173.9. I thought this was a little strange.

So is this the norm or is this just this box of 100? Im not gonna lose sleep over it either way just curious.

I also came across this post
http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Nu


edit for spelling </div></div>

I don't know what to tell you bro, but this stuff will make you goofy if you analyze it too much.

You have a batch of 56 heavies and a batch of 44 lighties. Why there is nothing in the middle, who the heck knows, but chalk it up to a statistical anomaly?

Still, a 2 grain spread isn't that much to worry about over a population of 100. Would have been better to have weighed them all right out of the box, or in the least, trimmed them down to a uniform length. I personally think that that's a pretty tight spread.

I've weighed brass, bullets, primers, all that stuff, but don't really do it as a rule. I ended up with too many odd-ball sized lots. If you compete for the brass ring, sure.

Chris

 

[TT]

Re: Weight distirbution of Lapua .308 Brass

You have a bi-modal Guassian distribution. Who knows why - could be due to different machines, materials, methods, measurements, etc. This is a classic six sigma problem. The only way to know is to perform a little RCA and perhaps some Design of Experiment...

 

[Pete E]

Re: Weight distirbution of Lapua .308 Brass

Of course the other issue might be your scales, not the brass!

 

[USMCj]

Re: Weight distirbution of Lapua .308 Brass

First thing, you dont weight sort fired brass, carbon buildup inside the case will give you false results. Second, you need to make sure all of the new brass is trimmed to the same length before you weight sort.

Having said that, a 2 grain spread is awesome! one of the main reasons people pay the extra bucks for Lapua brass. You would have a heartattack if you tryied to weight sort Winchester brass, out of a bag of 50, I had 7 grain spread. Nuff said!

 

[repiv]

Re: Weight distirbution of Lapua .308 Brass

Yes I have Bi distribution (cool term), my main concern is why? All the prep on all the brass is the same. Its not the scales, I have check against a balance beam scale. I did not have any reason at the time of purchase to weigh my brass. Its not part of my process.

Again Im not looking for a better way to do this in the future I most likely wont weigh brass as part of my process. I just did it this one time. I just thought it was really strange to have the "bi distribution" and from the other post I linked to I am not the only one.

 

[badbot]

Re: Weight distirbution of Lapua .308 Brass

the heavy ones were made on friday and the light ones were made the following monday

 

[repiv]

Re: Weight distirbution of Lapua .308 Brass

hehe BadBot that is exactly what I was thinking. Im gonna load them on a Tuesday and shoot them on a Saturday it should even out.................

 

[btm_54]

Re: Weight distirbution of Lapua .308 Brass

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: USMCj</div><div class="ubbcode-body">First thing, you dont weight sort fired brass, carbon buildup inside the case will give you false results. Second, you need to make sure all of the new brass is trimmed to the same length before you weight sort.

Having said that, a 2 grain spread is awesome! one of the main reasons people pay the extra bucks for Lapua brass. You would have a heartattack if you tryied to weight sort Winchester brass, out of a bag of 50, I had 7 grain spread. Nuff said! </div></div>
I would be tempted to FLS before trimming as well.

 

[USMCj]

Re: Weight distirbution of Lapua .308 Brass

Lapua brass doesnt need to be FLS out of the box, if the necks arent dinged up, I just neck size them and load away.

 

[repiv]

Re: Weight distirbution of Lapua .308 Brass

I will trim them after next firing and I may even weigh them again just out of curiousity but so far nobody has posted either that they have or have not seen this bi-distribution before.

 

[TimK]

Re: Weight distirbution of Lapua .308 Brass

I weighed my new Lapua .308 brass, and they were all within 0.5g. I wonder if your variations are somehow due to firing as another poster suggested.

 

[repiv]

Re: Weight distirbution of Lapua .308 Brass

I would not say its not possible. But I do follow the same process on the reloads. So nothing different has happened to the heavier ones than the light ones.

After next firing I will trim and re-weigh after a very good case cleaning and see.

 

[clmayfield]

Re: Weight distirbution of Lapua .308 Brass

I think the best time to sort by weighing is after brass prep and before firing. I would also think you would want to trim everything to the same length first.

Obviously, if you have the cases trimmed to different lengths, that will be a source of variation right there. If you have trimmed some and not others... there is your source.

 

[Unsichtbar]

Re: Weight distirbution of Lapua .308 Brass

With Lapua brass I stopped weighing, for all long range competitions were all shots are over 600 yds. A Brit Palma guy who is very good said he weighted the completed rounds, if they were in .5 for bullet case, powder, primer he shot those long range, thats what I do now for square range stuff. For tac matches and such I do not weigh brass or completed rounds.

IMO the best pay back for time spent on ammo quatity I have done is neck prep, annealing, polishing with brush and steel wool. Of course the basics such as position, trigger... is were 95% of my effort needs to be.