How much weight variation should be in Lapua 308 brass?

[jlow]

Generally pretty happy with this stuff but this has me worried. Opened two new blue box today and weight out 28 out of 100 from each box and found the following:

First box with Lot# P00648701/2583712 was pretty consistent with 26 out of 28 pieces weighting in between 170.80 grains to 172.58 grains so about a 1.78 grain variation (see below - Brass1). A couple of real heavy ones at 177 grains but I can live with that.

The second box with Lot # P00684405/1051613 is the one I am worried about. Looks like two separate lots with one lot around 172 grains and another lot around 173.5 grains, so with overall variation of about 3.38 grains (see below - Brass2). I weight each of the 100 cases afterwards and about half were over 173 grains.

Pretty disappointed as I was hoping to combine the two but that would mean if I want to keep under 173 grains will have to cull about 50 cases – is this normal? If not, would Lapua take the bad lot back?

 

[Steve Blair]

Re: How much weight variation should be in Lapua 305 brass?

Just a suggestion: reverse your axes to better show the distribution.

 

[jlow]

Re: How much weight variation should be in Lapua 305 brass?

Seems pretty obvious?

 

[jlow]

Thanks! I made the change....

Yes, I actually always weigh them all but that was the result from a survey to figure out what i had. For the survey, I actually write down the number so that I can figure out the binning interval to use. When I actually bind them, which I did for the poorer lot, I do not write down their weight but only use the number to figure out where to put them in the bins.

 

[Steve Blair]

Here's a test I did with Lapua Palma brass. Note that the X axis is weight and the Y axis is quantity. This shows the distribution more clearly as two distributions within the sample population.

 

[jlow]

Steve, I understand what you mean, but our two graphs actually show two different things.

Your graph is the correct one to show distribution but remember that you are actually showing the number of cases at each weight range.

My graph is a simple bar graph with case number (i.e. 1 to 28) not number of cases, vs. their specific weight. So very different graphs.

Mine was just a quick and dirty one for me to see how even the weight distribution is. I weight each piece, put the number in Excel, sort the number by weight and inserted a bar graph based on their weight alone, Excel supplied the case number.

It is certainly not the ideal way to plot the data but they were for different uses.

 

[jlow]

So to follow up, from looking at your actual numbers, it appears that you are seeing the same two lot distribution with what I assume is also Lapua 308 brass? That is unfortunate…

Am I right then to assume that they cannot do any better, and shooters just have to buy enough brass so that they can segregate them and shoot them as two different lots?

 

[Canadian bushman]

Ive sorted three hundred 308 brass with variance under 3 grains with the majority favoring half that. I culled 20 for testing.

All brass was deburred neck turned and washed before weighing.

 

[savagedasher]

I don't care how much a case weighs . The reason being it all is relative to the machining process . Extractor width and depth thickness of the head can make a case weigh over a grain difference.
To me I feel the internal capacity.is the way a case should be checked. You can take two cases with the same external size and weigh the same. Then check internal Capacity and find 1 full gr difference. Larry

 

[CatShooter]

Jlow...

I once sorted 1,200 pieces of Lapua 308 (brown box) and except for 9 pcs, the rest were inside of <3 grains.

This past summer, I sorted almost 800 pieces of R-P 222 Magnum brass, bought over a time span of 20 years, and all of them were inside of <3 grains... and the fell inside of two lots that were <1 grain each.

So I think that is a lot.

 

[Steve Blair]

So to follow up, from looking at your actual numbers, it appears that you are seeing the same two lot distribution with what I assume is also Lapua 308 brass? That is unfortunate…

Am I right then to assume that they cannot do any better, and shooters just have to buy enough brass so that they can segregate them and shoot them as two different lots?

[br]
This is common with Lapua brass. Oddly, Winchester brass, of much lower overall quality, does not seem to show this characteristic. I stopped weighing brass after performing a series of accuracy and chronograph tests that convinced me the effect is negligible. YMMV

 

[CatShooter]

I don't care how much a case weighs . The reason being it all is relative to the machining process . Extractor width and depth thickness of the head can make a case weigh over a grain difference.
To me I feel the internal capacity.is the way a case should be checked. You can take two cases with the same external size and weigh the same. Then check internal Capacity and find 1 full gr difference. Larry

Weight IS volume... how much do your extractor grooves vary? Mine are within a ~thou or so... not worth bothering about. And thickness in the head... that is why you weigh them.

You cannot measure volume unless you first put the case is something like a trim or body die so the walls are always held in the same place, and that is a pain with water.

I measured a bunch of fired cases by "volume". Fired them, sized them, measured them... then I fired them, sized them, and measured them again - they were all over the place. Try it yourself and you will see what I am talking about.

 

[watercam]

I have to agree with Steve. I tested loads with lightest vs. heaviest brass at 1000 yards and could not see enough vertical to worry about - assuming it wasn't me (which it probably was). I still sort the loaded rounds (a la Audette)
so that there is never more than .1 grain difference between one round and the next but I will probably stop that as well. I am not saying anyone should not prep cases to their hearts content though.

 

[jlow]

Yea, as you say, it is odd that Lapua still have this distribution problem vs. Win brass. Some of it is significant like the two 177 grain cases which is close to a full 7 grains heavier than the light one in the bad lot….

Just going by the article “How Cartridge Brass is Made” on this website, seems like easy enough to start off with blanks that are close as the only thing one has to be sure of to start is the thickness of the brass sheet you start off with and the ID of the punch that makes those blanks, so one would think that after the case is extruded the only thing that is left is trimming and primer pocket forming which can affect weight and its hard to understand how that much weight variance can creep in.

Sorry Steve and MTM, I would very much like to believe that weight makes no difference but apart from my own work which shows a correlation between weight and volume, how quickload shows the effect of case volume on chamber pressure, and the wide variance i.e. 7 grains shown here. It’s hard for me to feel comfortable ignoring weight.

 

[CatShooter]

On another note: Catshooter has stated many times on this forum he does not own or use full-sizing dies. With that I can believe he gets some corky experiences to volume consistency. I get very good volume consistency myself, when the die matches the chamber and is setup right. But of course a poor match up between the die and chamber, or setup, could also cause corky consistency.

My 2-cents
Donovan

Well.. I own a few FL dies, but only because I was given brass from other guns, or rebarreled in the same caliber. My cases fit the chambers very well... snugly.

My style of shooting does not requite shooting fast in a rest, where the gun cannot be disturbed.

 

[people]

Seems standard for the Lapua I have bought over the years. It shoots great in my rifles I shoot it in but weights are all over the place and checking case wall thickness and wow is all I can say. Not just a little bit of difference but huge swings in both lots I have bought. Out of the 900 cassings maybe 50 measured 0 thousandths. Most were .003 to .006"

I read the article Mr. Salazar posted so I figured I would test. Just because. I am happy with how my 308's shoot and am not too concerned on the banana effect. I mainly shoot steel and rocks with my 308 so a little slop is ok.

I do care with my 300WM. I bought 500 Win 300WM brass and a shocking number was measured at .000 and less than .001 inches. I just went and looked at the bags.

Over 100 were .000 to <.001
under 300 here .001 to <.002
over 100 were .002 to <.003
8 were .003 to <.004
1 was .004 to <.005

I have never measured my Lapua 338 brass as I am very happy with it and am not wanting to play head games with my self.

 

[chkunz]

Has anyone tried to determine what case weight variation is worth on the target? I have seen a lot of claims over the years that it is important and other claims that say it is not important but I can not remember anyone that presented meaningful data either way. The new F Class target has touched off a new arms race and is pushing accuracy to a new level so the answer for F Class might be different than a less demanding target.

 

[CatShooter]

Has anyone tried to determine what case weight variation is worth on the target? I have seen a lot of claims over the years that it is important and other claims that say it is not important but I can not remember anyone that presented meaningful data either way. The new F Class target has touched off a new arms race and is pushing accuracy to a new level so the answer for F Class might be different than a less demanding target.

I started to do something with this a few years ago, and ran into the problem that today's chronos do not have the ability to discern such small changes repeatably.

My gut feelings is that with variations of more than 3 grains, you will see it in the vertical at long ranges on a calm day, but that is a feeling, not a proven fact.

For long ranges, I would keep cases within a 2 grain window, if for nothing more than the psychological effect.

 

[savagedasher]

I don't care how much a case weighs . The reason being it all is relative to the machining process . Extractor width and depth thickness of the head can make a case weigh over a grain difference.
To me I feel the internal capacity.is the way a case should be checked. You can take two cases with the same external size and weigh the same. Then check internal Capacity and find 1 full gr difference. Larry

Weight IS volume... how much do your extractor grooves vary? Mine are within a ~thou or so... not worth bothering about. And thickness in the head... that is why you weigh them.

You cannot measure volume unless you first put the case is something like a trim or body die so the walls are always held in the same place, and that is a pain with water.

I measured a bunch of fired cases by "volume". Fired them, sized them, measured them... then I fired them, sized them, and measured them again - they were all over the place. Try it yourself and you will see what I am talking about.

My cases hold 41.6 to 41.8 grains of water. After sized and trimming The same cases after 10 reloads will have about 1 tenth of a grain more water capacity due the thinning of the brass. I just random check the total of the case weight. .06 difference. The internal water capacity was the same as it was 6 firings ago.
OL with the powder I use and the internal water capacity of 41.80 my pressures is 62608 and the speed of 3103 my gun shoots 3095 when I change cases to 41.6 the pressure listed on QL is 63398 and the speed of 3110 My gun shoots 3105. Internal case volume is all that matter to me. Larry

 

[Canadian bushman]

Internal volume should be measured after firing and before sizing.

The sizing process can taint your findings whether fl or ns.