case weight

[barrels]

Thanks to all on the forum, I read on a daily basis. I have learned alot

I am currently weighing all my cases in part of preparations for reloading. I weigh all the cases in the lot and remove the top and bottom 25% for another loading group and keep the middle 50%. This typically gives me a case variation weight range of .5 grains

Is this necessary?


Thanks

Eric

 

[bheadboy]

I weigh all cases in a lot, and line up on a paper with weight in gr. - they form a pyrimad of sorts with high numbers in the central weights.

i then take the largest number by weight and those +/- .3gr and that is my lot to keep for serious shooting.

The extreme heavier and lighter ones i set aside in siplock to have for another test, often they willmix well with another lot.

i can also use them for breaking in a new bbl, beginning a ladder test (not thefinal tuning) -hunding in area where shots are shorter and may loose a case.

Bob

 

[spclark]

I weigh all the cases in the lot and remove the top and bottom 25% for another loading group and keep the middle 50%. This typically gives me a case variation weight range of .5 grains. Is this necessary?

Necessary? No. They'll all work fine as they come out of the box.

Worthwhile? Yes, depending on the shooting discipline you'll be using them for (BR, high power, varmint, silhouette, groundhogs / prairie dogs, long range, etc.) and your tolerance for accuracy.

The smaller the 'group' you expect your equipment (hardware + ammo) to shoot, the more important everything becomes that can / will affect accuracy and consistency.

 

[barrels]

Thanks for the replies.

I am target shooting from a bench and working on accuracy shooting. I have been handloading for a year or so and a have a good mentor for reloading. I completely uniform the neck, primer area, flash hole and control my powder load. I just could not wrap my mind around the"necessity" to have the same weight casings.


Thanks for reenforcing my process.

 

[FroggyOne2]

I weigh them, then shoot them in order from the heaviest to the lightest.

 

[nam72]

A question : would filling the cases by volume/cc.. be better? Like using a once fired case ,to start with.It seems to me ,it would actually check one case against another more precisely.. I've been weighing cases forever,but I like to experiment. Think I'll try it on about 20.In my case, I have to form my cases and the neck is thicker. It's important that I have good cases to begin so not to wrap up time in marginal ones. Note: that's because I made many mistakes over the years..

 

[mikecr]

H2O capacity checks are absolutely better.
To prove it(if you need proof), load 5 fireformed cases which are neck sized only and fire across a chronograph.
Then heavily FL size those 5 cases, reload & shoot across a chrono.
Same weights, different volumes, different velocities.

And when someone suggests that Diddly Smith won a trophy & he weighs cases,, consider how well he might have done if he had actually measured and matched his capacities.
He might also have done better if he actually weighed his powder, made straighter ammo, or just stopped taking shortcuts in general.
We'll just never know..

On the flipside, all the efforts in the world won't make shooting a bad barrel payoff.

 

[moosetracker]

+1 Mikecr

Check the following thread for more in-depth discussion.
http://forum.accurateshooter.com/index.php/topic,3761214.0.html

 

[tripcrow]

Don't know why 2 of my posts are empty in that thread.

But here's the results of a test I just did on a bag of 308 WW cases that were sized to 338 Federal, fired once, full length sized, trimmed to length, necks cleaned up, sonic cleaned, weighed, weighed again with a primer, then weighed again at least twice each when filled with water. The scale was a Acculab 123. I used the flat side of a knife to skim the filled tops even.

I figured the biggest part of the discrepancy between case weight and case volume was in the case's web thickness. So I had a tool made up to measure that. But that didn't turn out to be anywhere near linear.

Here's the case weights without the primer and that case's H2O capacity average weight.


152.54- 59.26
153.28- 58.96
153.30- 59.02
153.50- 58.84
153.52- 58.96
153.54- 58.87
153.56- 58.76
153.60- 58.90
153.64- 58.84
153.94- 58.74
153.96- 58.73
153.98- 58.76
154.02- 58.72
154.06- 58.74
154.08- 58.63
154.10- 58.63
154.10- 58.70
154.30- 58.58
154.30- 58.48
154.32- 58.52
154.36- 58.64
154.36- 58.54
154.44- 58.61
154.54- 58.68
154.56- 58.65
154.58- 58.64
154.60- 58.59
154.62- 58.56
154.68- 58.75
154.72- 58.65
154.74- 58.65
154.76- 58.67
154.78- 58.79
154.84- 58.73
154.84- 58.66
154.84- 58.62
154.84- 58.59
154.86- 58.69
154.98- 58.80
155.00- 58.70
155.04- 58.65
155.08- 58.62
155.26- 58.56
155.30- 59.32
155.36- 58.66
156.20- 58.60
160.34- 58.06
162.32- 58.03

 

[tripcrow]

The 48 cases above had an average weight of 154.68g and an average water capacity of 58,69g. If you were to split the 48 cases into groups of 12 by weight. The lightest 12 weighed on average 153.53g and had an average water capacity of 58.89g.The next heavier 12 were 154.25g with a capacity of 58.62g. The next 12 were 154.71g with 58.66. And the heaviest 12 were 156.22g with a 58.61g water capacity. To put those in order:

153.53g - 58.89g.
154.25g - 58.62g
154.71g - 58.66g
156.22g - 58.61g

The extreme spread of all 48 cases is 9.78g of weight with a spread of 1.29g of capacity. If you were to sort out the lightest 6 and heaviest 6 cases you'd have an extreme spread of 1.48g of case weight and .42g of capacity. Better yet taking out both the lightest 12 cases and the heaviest 12 cases leaves you with the middle 24 cases having an extreme weight spread of just .46g and a capacity extreme of .31g.

What's it all mean? Using all the cases would give an inherent velocity spread of approximately 26 fps with a full load of powder. By sorting out the lightest 6 cases and heaviest 6 cases the inherent velocity spread caused by unequal case capacity can be reduced to 8 fps. Taking out the lightest 12 and heaviest 12 reduces the inherent velocity spread to 6 fps.

I do not know how closely the culling used in the above examples would match up with other cases. But I do have results from other weighings that just need to be inserted into Excel to make sense of. Was saving that for this winter. But from just these results I'd guess that sorting out both the lightest 12% and heaviest 12% of your cases is going to cut down inherent velocity spreads to an extremely low amount.

 

[markm87]

I've been pooring over the Technical Articles on this site. I've gathered that case weighing is one of the least productive activities in chasing accuracy. I think it was in a "Froggy" article.

 

[tripcrow]

I think it depends on how you sort after weighing. Sorting out the extreme light and heavy cases seems to have a very positive effect. Lately I'm starting to think that if you're seating your primers correctly, uniforming primer pocket depth is the biggest useless exercise. Except that using a good tool will make the corners of the pockets nice. But I was saving those tests for this winter too.

 

[mikecr]

Bill your testing very useful, and it could be taken further.
You can see with your results that there is not a direct relationship between case weight and capacity.
That is, only in a general sense does increased case weight result in decreased capacity.

I assume you used QL to derive the velocity spread potential.
And this shows a potential ES contributor from doing no culling at all.

You could now derive a velocity spread from the largest disparity between matched weight cases that still show actual capacity variance. With this, it could be shown(as an example) the ES contributor missed by those who match up only by case weight(not capacity).

Another test is to measure capacity with fully prepped and fireformed cases, capacity matched, that have not been FL sized -vs- those that have been.
There would likely be an ES contributor introduced here as well -based on the capacity variance introduced by FL sizing(a smaller amount).
I am confident that actual capacity matching is only possible with fully prepped and fully fireformed brass that is not FL sized.

As far as primer seating, there is a great deal to learn there. A lot of potential tests with big payoff potential.
Primers seated ~flush
Flush primers seated X-distance from striker
Primers seated to x-crush
Crush primers seated X-distance from striker
Striker overall energy at impact(mass/pushing force)
Striker speed at impact
X-mass at x-speed striker
Primer hardness
With atleast one gun of mine, a 10thou adjustment to the firing pin distance(either direction from boltface) significantly opens grouping, while still reliably firing, even in cold conditions.
I had to find a sweetspot with it due to a setscrew failure. When I did, my groups were cut by a solid 1/4moa! The only other factor that could affect this gun so much, is seating depth changes.
So don't rule out primer/pocket adjustments without looking into it.