Somewhat Disappointed - Lapua Brass

[ALO]

I received a 100 box of Lapua 223 the other day and was a little disheartened when I started to weight them. Weights were from 93.9/94.00 all the way up to 96.8 and above. Between this 2.8 grain swing, everything in between was also "not very consistent". 94.2 and below 10 cases, 94.3 to 94.6 13 cases, 94.9-95.3 28 cases, 95.5-95.9 8 cases, 95.7-95.9 13 cases, 96.0-96.1 12 cases, 96.3 to 96.5 12 cases, and 96.8 and over 4 cases. If I were accumulating cases for match shooting, I would be inclined to use the 94.9 to 95.3 gr. cases or 95.7 to 96.0 cases. How critical are cases weights when it comes to accuracy? Am I just wasting my time by weighing case? These cases are brand new cases and have not been fired or trimmed. I guess I was expecting a little more consistency with Lapua brass, but it is still the best out there!

 

[finnaddict]

Measure them.

 

[Panzer22]

Load them, shoot them then size and trim and do whatever other prep you do, then weigh them. Sort to groups within a grain, go from there. Within a grain is going to be fine, and really depending on what your doing might be OCD.

 

[Raythemanroe]

I found some Norma brass for my 300 wm and about 75% were a grain or less variance.

 

[Raythemanroe]

Load them, shoot them then size and trim and do whatever other prep you do, then weigh them. Sort to groups within a grain, go from there. Within a grain is going to be fine, and really depending on what your doing might be OCD.

This is very true, can't really say how close they are until your do your part.

 

[ALO]

Thanks, these was my next steps. I guess I was just expected a little more consistency with Lapua Brass.

 

[broncman]

Weight means NOTHING!

Unless you are checking internal case capacity you are wasting time. Somewhere on here, someone proved this by measuring case capacity of the different weights and the results were surprising. Keep snipping a pirce of brass from a case neck till it weighs what your extreme spread is. You will see that small amount of brass can easily come from the extractor groove machining etc.

Take your lightest cas and heaviest case, measure capacity and go from their if there is a difference....

 

[savageshooter86]

I've done it and I am almost certain Donovan has done so with more precise than I did. I picked 10 cases that weighed the same and then measured h20 capacity. IIRC only 2 had same h20 and the others were all over, and as much as 3 grains variance

 

[finnaddict]

http://forum.accurateshooter.com/index.php?topic=3827223.0

 

[jlow]

So interesting question as I have also just brought and weight sorted 200 Lapua 223 brass this week. My results out of the box are very similar to ALO’s i.e. the average weight from the two boxes were 95.25 gr and 95.14 gr respectively. Weight variation was 2.58 gr and2.52 gr, and the max and min weights were 96.36 gr/94.78 gr and 96.42 gr/93.90 gr respectively.

I know people here don’t believe that weight has anything to do with volume, and I agree that volume should only be determined after firing but in the past at least with LC09 223 brass, I have found good correlation between weight and volume (after firing). Measuring 20 cases by both weight (2x with Gempro 250) and volume (3x each with rubbing alcohol) The correlation coefficient between the two numbers was 0.72 and BTW 1.0 is a perfect correlation.

Have not done this with the LaPua as they are yet unfired but my question is the same i.e. what effect will weight or for that matter volume variance will have on precision/accuracy? For example, we know for a fact that case with thicker walls i.e. like an LC 308 case will need less powder as pressure will be greater for the same load. So when one uses cases with this much weight/volume range even if one does load development with say a batch of cases in say the lower weight/volume, would one be in danger of moving out of a node say as one use higher case weight/volume?

 

[BoydAllen]

This is a little off topic, but speaks to the issue of consistency of a different type. A friend, who shoots Lapua brass in his .223, noticed significant variation is bullet seating force, when seating with a Wilson die and arbor press. (This setup gives more sensitivity than a reloading press.) Using a Hornady annealing kit, and a metronome to give an audible count, he was able to do a consistent job of properly (not over) annealing his cases. Seating force became much more consistent, and accuracy improved significantly. The reason that I mentioned this is that your weighing of cases shows an attention to detail that I thought might be usefully directed in a different direction. Obviously paying attention to case volume, is a good idea, that grows in significance with the increase in shooting distance. The improvement that my friend saw was readily seen at 100 yards. After your first firing, sizing and trimming, I would sort by weight, take a look at variation in seating force. Weight may not be a perfect indicator of volume, but within the same lot of brass, I think that the correlation is useful.

 

[broncman]

It can be confusing, buy volume is the only TRUE way to insure uniformity. As savagshooter pointed out, there was a variance in voulume in even the same weights of cases!

Depending on the powder , powder can take up as much as ten times the space per grain as 1 grain of brass. So if the weight difference came ONLY from the inside of a case.....1 grain of weight difference would make about .01 grains of powder difference.....but that would be in a perfect world!

Where does the extra weight come from? Outside dimensions somewhere or inside?

Measuring inside with a liquid by volume is the inly reliable way to know!

 

[Raythemanroe]

Sorting by volume does not insure uniformity, sorting by volume only insures volume. You can have a egg hold the same volume of a square box..The same volume may be more important to consistent pressures then uniformity.

 

[broncman]

Sorting by volume does not insure uniformity, sorting by volume only insures volume. You can have a egg hold the same volume of a square box..The same volume may be more important to consistent pressures then uniformity.

uniformity of volume to acheive uniformity of pressure is what you are after correct??? granted, uniform neck clearance etc is great..but we are really talking about volume and related pressure in this thread??

One reason a good load that holds good ES over several tenths of a grain is awesome to have...then small case capacity changes makes less difference


But to clarify my earlier statemont in uniformity....yes ray you are right...measuring volume only insures uniformity of volume alone...

 

[XTR]

Unless you are shooting BR, or longer than 600 yards I don't think you need to worry about weight, what type of shooting are you doing? If it's service rifle that's a HUGE X/10 ring, if you don't hit it it's because you weren't pointed at it. If it's 600 yard F class you may be able to see some difference, if you are shooting shorter distances I wouldn't worry about it. Then remember that the whole point of the OCW testing to find a load in a node that's not sensitive to minor variations in load or volume (i.e., pressure)

You'd probably be better off (and have piece of mind) proving it to yourself by loading up 10 of the heaviest and 10 of the lightest, shoot two 10 shot groups and see if there is any difference.


Now, as for weight to volume comparisons; someone here did one with a good sized sampling and it did show that there was about a 70% statistical correlation between weight and volume.


You know that reading too much about reloading on the internet will give you a twitch right?

 

[jlow]

So those who might be interested, here is the statistics from weighting 100 pieces of Lapua brass from two different batches and one 100 pieces of LC11 brass:

Lapua1 Lapua2 LC11
Average weight 95.26 95.14 92.09
Range 2.58 2.52 2.36
Percent variance 2.71 2.65 2.56
SDEV 0.60 0.60 0.53
Max weight 96.36 96.42 93.04
Min weight 93.78 93.90 90.68
N size 100 100 100

So one can conclude from this is:

1) Lapua brass is on the average 3 gr heavier than LC11 brass.
2) The heaviest LC11 brass weight less than the lightest Lapua brass.
2) Lapua brass from one batch to another has little variance.
3) LC11 brass weight variance is actually slightly less than Lapua but it is such a small difference that it is not statistically significant..

 

[mikecr]

Let us know when you have results for H20 capacity on these cases

 

[XTR]

So one can conclude from this is:

1) Lapua brass is on the average 3 gr heavier than LC11 brass.
2) The heaviest LC11 brass weight less than the lightest Lapua brass.

These two are probably worth noting. Because LC 308 brass is heavier than just about any commercial brass lots of people think the same is true of LC 5.56/223 it's not. I think there are a number of online posts/reports that show that LC is lighter in almost all cases.

 

[jlow]

The other stats that is important and I don't have data for yet is how concentric the neck thickness are i.e. how much culling needs to be done. Hope it is as good as my 308 Lapua which was zero.

Still sure wish someone will chime in on whether eight/volume can move you out out of a node........

 

[mysticplayer]

If the variation in case weight IS due to change in internal volume, it will affect the combustion volume which affects pressures which affects tuning, etc, etc.

How much? That varies with case volume, powder and all sorts of other stuff. Which is best tested with holes in paper then trying to monkey brain the physics.

For me, I check the volume of a sample of the brass I use after fireforming. If the volumes varies, I use other brass - way too expensive to be wasting time with wonky brass.

I do not weight cases.... machining of extractor grooves can throw your weights way off.

I also do not shoot Lapua brass.

Consider, neck turning, annealing, volume checks to get best performance from any brass.

Personally, given how small the case volume is already, the last thing I want is to reduce that further. Win brass has worked for me and it is readily available.

For the 223 and LR F class type shooting, I can see changes due to 0.1gr variation in powder charge. The last thing I want is a component that may affect that making tuning that much harder.

Jerry