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Weighing components

 
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  #29  
Old 03-29-2010, 05:28 AM
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Re: Weighing components

Quote:
Originally Posted by MontanaRifleman View Post
If there are guys like Speedy out there who are getting good results without weighing capacities, I would think that would be a compelling argument for it's lack of necessity.
It only makes me wonder how he would have done had he done capacity checks, & weighed his powder.

I know for a fact that brass weight does not always correlate to capacity. I also know that capacity variance affects ES.
So I cull by H20 capacity checks after fully fireforming.
I see weighing brass as a poor shortcut.
And I see generalizations about what anyone in competition is/isn't doing, in the same light.
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  #30  
Old 03-29-2010, 10:28 AM
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Re: Weighing components

Quote:
Originally Posted by 400bull View Post
I have been reloading now for a couple years but have never sorted my reloading components by weight. Up until this past week all that I used to weigh out my charges was a balance scale. It took too much time to weigh each component to make it worthwhile to me. I reload more for the cost savings then the accuracy although I do strive to get groups under 1 ½ @ 100 yards. This past week I picked up an inexpensive digital scale that seems to be Accurate to +/- .1 grains. I decide to go through and measure all my previously loaded rounds to see how consistent they are. I was very surprised to see extreme spreads of 15 grains. Meaning that when I weight the finished rounds I am +/- 7 grains from the average weight. For those of you that do sort your components by weight what kind of normal weight swings do you get? Do you thing that sorting your components by weight is worth it for hunting accuracy out to 500 yards?

400bull
Well now that this post has turned into a dog pile to anyone that has a different opinion
it looks like you will have to just try sorting and see if it helps.

Due to differences in fire arms the best way to measure results is to chronagraph your loads
before and after weight sorting to see the change in Standard deviations. Groups @ 100 yards
is the next best because of minimum effects of wind, mirage and shooter problems. after getting
results then you need to move out to 300 to 500yards and do the test all over again (Before
and after sorting).

If it does not make any difference then don't worry about it.

There have been a lot of discussions on this subject and opinions vary so you have only one
option left . To try or not.

This is a great site to learn from as long as you don't already know everything there is to
know. so don't let the gang bangers that jump on a guy like BB that has probably forgot more
than they will ever know because they will not open there minds to different approaches to a
problem or method of doing something.

Good luck on your quest for better accuracy.

J E CUSTOM
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  #31  
Old 03-29-2010, 04:58 PM
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Posts: 675
Re: Weighing components

Just for interest has anyone done any calculations to work out how much the volume changes when the mass changes.
The density of brass is 8.4 to 8.7g/cm3. This 129.631 gr/cm3.
The density of brass changes due to the ratio of copper to zinc changing. I am not sure of the density of rifle brass
A 1 grain difference in weight is a 0.77% difference in volume.
Anyone used Quickload to see how this much difference in case capacity(volume) changes pressure/velocity etc?

My gut feeling is if you want to know case capacity then measure the case capacity, but be aware that the density of water changes with temperature.

Stu.
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  #32  
Old 03-29-2010, 08:28 PM
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Re: Weighing components

Quote:
Originally Posted by kiwi3006 View Post
My gut feeling is if you want to know case capacity then measure the case capacity, but be aware that the density of water changes with temperature.
Stu.
I agree

This can be for RELATIVE case culling, or ACTUAL capacity(well, close enough).
Both are useful.
The result can be manually entered in QL to dial in a load, and further tweaked to match chrono readings.

Brass weight departs from capacity conversion because some of the brass does not contribute to capacity, and it doesn't take much to leave the pack given it's density.
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  #33  
Old 03-29-2010, 09:24 PM
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Re: Weighing components

Weighting cases on the assumption that there is a constant correlation between case weight and internal volume is a complete waste of time that is based on an erroneous assumption. Others factors such as dimension of base and extractor groove are significant confounding variables.

With new brass, I expand necks to uniform size, turn them for uniform thickness, trim to uniform length, chamfer, clean primer pockets and deburr primer holes. After fireforming, I routinely measure internal volume of 30 cases in order to adjust Quickload parameters to customize it my firearm. I have done hundreds of these measurements and I have found that even with the best of brass (Lapua), the correlation between case weight and internal volume is extremely weak and typically less than 50% valid.

To illustrate the point here's a sample of 30 fireformed Remington cases in my 338 Edge. All cases have been prepped as described above. The empty and water-filled cases were weighted on an Acculab VIC 303 that is accurate within .001 gram or .02 grain.

#.....Case weight (grs)……Var. %……..Water weight (grs)….Var. %
1…….272.68……………………-1.19%.............116.66…………….-0.04%
2…….276.74……………………+0.28%............117.00…………….+0 .25%
3…….272.68……………………-1.19%.............117.10…………….+0.34%
4…….267.24……………………-3.16%.............117.48…………….+0.66%
5…….278.84……………………+1.04%............116.18…………….-0.45%
6…….276.24……………………+0.10%............116.62…………….-0.07%
7…….278.14……………………+0.79%............116.12…………….-0.50%
8…….276.22……………………+0.09%............116.56…………….-0.13%
9…….280.58……………………+1.67%............116.24…………….-0.40%
10…..276.48……………………+0.19%............116.40…………….-0.26%
11…..276.58……………………+0.22%............116.50…………….-0.18%
12…..276.76……………………+0.29%............116.64…………….-0.06%
13…..279.64……………………+1.33%............116.64…………….-0.06%
14…..278.16……………………+0.80%............116.80……………+0 .08%
15…..277.18……………………+0.44%............116.78……………+0 .06%
16…..277.60……………………+0.59%............116.64…………….-0.06%
17…..275.82……………………-0.05%.............116.82……………+0.10%
18…..271.74……………………-1.53%.............117.20……………+0.42%
19…..276.40……………………+0.16%............116.72……………+0 .01%
20…..271.68……………………-1.55%.............116.86……………+0.13%
21…..275.62……………………-0.12%.............116.94……………+0.20%
22…..276.32……………………+0.13%............117.22……………+0 .44%
23…..276.00……………………+0.01%............116.96…………... .+0.22%
24…..278.02……………………+0.75%............116.74……………+0 .03%
25…..273.90……………………-0.75%.............116.54…………….-0.14%
26…..278.00…………………..+0.74%............116.52…………….-0.16%
27…..275.60……………………-0.13%.............116.10…………….-0.52%
28…..276.62……………………+0.24%............116.74……………+0 .03%
29…..275.44……………………-0.19%.............116.74……………+0.03%
30…..275.94……………………-0.01%.............116.72……………+0.01%
Ave..275.96………………………..…………………....116.71

Using the 0.5% variation standard normally advocated (+ or - 0.25% from average), one would have selected 13 of the 30 weighted cases. Selecting by internal volume would have resulted in 20 retained cases. Moreover, 3 of the cases selected by weight would have been rejected by volume (#10, 22 and 27). Consequently, selecting by weight would have resulted in the identification of 10 of the 20 cases that had relatively uniform internal volume.

If one looks at the validity of the assumption of case weight as an indicator of internal volume within a 0.5% variation, it would appear that the assumption is dubious at best. For example, you would expect case #1 which weights 1.19% less than the average of 30 cases to have approximately 1.2% greater internal volume than the average volume for the same cases. Instead, that case is almost perfectly on the mark for case volume (-0.04%). Indeed the correlation is valid only for 11 of 30 cases (#6, 8, 10-12, 17, 19, 21, 23, 29 and 30) or 36.7%.

Another interesting observation from the table above, is that the weight variation among cases is quite large (-3.16% to + 1.67% = 4.83%), whereas the internal volume is relatively constant (+0.66% to -0.52% = 1.18%).

I and 2 of my shooting buddies have run this same experiment independently with hundreds of cases, using 5 different brands of brass (WW, RP nickel, RP, Hor., Lapua and FC) and 6 calibers (223 Rem, 6.5x284, 308 Win. 300 WM, 338 WM,338 Edge) and have come to the same conclusion. That is, if you wish to sort brass for consistency, do it by measuring internal volume.

I apologize for the long post.
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  #34  
Old 03-29-2010, 10:20 PM
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Re: Weighing components

Thanks for the post Moostracker. Very enlightening - nothing like actually looking at some real data. I see the total max water weight volume variance (high vs low) for these Rem cases was just over 1% Most of them were fairly close. Did you mark the cases and record firing data to see if there was any correlation of performance between the upper and lower end?

-Mark
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  #35  
Old 03-29-2010, 10:25 PM
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Posts: 2,598
Re: Weighing components

Quote:
Originally Posted by J E Custom View Post

This is a great site to learn from as long as you don't already know everything there is to
know. so don't let the gang bangers that jump on a guy like BB that has probably forgot more
than they will ever know because they will not open there minds to different approaches to a
problem or method of doing something.

Good luck on your quest for better accuracy.

J E CUSTOM



Apparently you are only open to the opinion of those that agree on wieghing cases.
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