Weighing Cases to enhance accuracy?

C

Cowboy4

Guest
What is the acceptable variation between case weights that is used by those who sort by weight?
I'm developing loads for a 257 AI, and would like to remove as many of the known variables with my cases as I possibly can. The acceptable case weight spread will help me.

Thanks.
 
I sort my cases to as close as my scales weigh. But just as important is to keep track of the number of firings per case,so that 2 times fired doesn't get fired with 5 times fired where neck tension would be different. Consistent neck tension is of utmost importance. Of course everything you can do to be consistent is important! Remember this: accuracy is the results of consistency!
 
Cowboy4 said:
What is the acceptable variation between case weights that is used by those who sort by weight?
I'm developing loads for a 257 AI, and would like to remove as many of the known variables with my cases as I possibly can. The acceptable case weight spread will help me.

Thanks.
Click to expand...
for a hunting rifle .3 to .5 is good.For 1k I go to .1 .check your cases after all prep work is done,this makes a big difference.the more brass you start with the better brass you will end up with.I start with 500 then prep and weight them all.I am shooting brass done 2 years ago.:D
 
Acceptable Shell Lengths

As long as we're talking acceptable WEIGHTS - what about acceptable LENGTHS for precise long range target shooting?

Tomorrow my new PEDERSOLI SHARPS QUIGLEY 50/90 will be delivered, and I'm trying to get some loading started. BUT I'M BRAND NEW, AND DON'T MUCH KNOW WHAT I'M DOING.

I bought some new STARLINE 50/90 brass - which is supposed to be 2.50" in length, but none of them are. They average around 2.49". And again, please, I'm talking precise long range target shooting here.

Should this bother me?

Thank you very much.
 
There is an awful lot of typewriter accuracy on any internet site. Why don't you weigh your cases, and take one set that is as close as possible, and another set that is as far away as possible.

Now, either shoot groups -- which allows for bias, or shoot them over the chronograph. The whole notion of weighing cases is that the ones with "more weight" have "less volume", and will therefore have a slightly higher velocity with the same powder charge. See if that notion is true. If you're using good brass, I'll bet you'll find that velocity variations don't correlate with absolute brass weight all that well. That leaves you in the "can't hurt" category (unless like me, you have a low threshold for boredom).
 
Thank you very much, Charles E -

Does your reply mean "no"?
 
No, it doesn't mean "no." I use pretty good brass, RWS or Lapua or Norma. I did my little test, and found no direct correlation between case weight variance and velocity. With the big cases I shoot, a 3-grain difference in weigh showed no correlation.

As far as velocity variance from all possible causes, it is hard to get a low enough variance not to show up at long range as vertical stringing, which is why we have to tune the load. The first level of "tuning" is for accuracy -- what kind of powder, what bullets, etc. The second, and what we are almost always talking about on this forum, is "tuning out, the vertical." When you get this tune, it doesn't really matter what the velocity spread, as long as it is reasonable.

For example, I remember Steve Shelp doing a lot of testing, and he found that the most accurate powder he could come up with for his .338 Yogi didn't give as low a velocity spread as another powder. With the higher ES/SC of the more accurate powder, he had a little more work in load development, but when done, he a very accurate combination.
 
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Well if I can put my 2 cents in here,I beleive Charles is right. I have done extensive testing on weighing cases and found it to not matter. Alot of old timers will tell you this is the way. I have even went as far as to measure the volume inside the case. Like charles said you can take 5 that weight the same and 5 far apart and they will shot the same. I invest 1000 dollars in a wireless camera to see if the same ones go out each time at 1000 yards without any luck. I think instead of weighing cases, spend more time on the necks,making them the same thickness,true,and neck tention. I have found this to make more differance than weight. Someone said above to keep them sorted by how many shots are on them,this is very good advise. I also found the best practice is to use new brass every match,costly but effective...Shannon
 
Here is a bit of real data I did recently

I sorted 1000 RWS 8x68s cases and got the results below. I took the 5 lightest and the 5 heaviest, prepped them and loaded them up. I shot them through my chronograph while fire forming them.

Light
3089 (clean barrel)
3110
3118
3119
3120
Mean 3111

Heavy
3138
3110
3130
3140
3139
Mean 3131

These data seems to indicate weight does matter "some".


I then took the 277.6 ones and sorted them on a scale accurate to .05 grains. I got 48 that were 277.55. I necked them down and turned the necks (~.95 grains), trimmned (~.15 grains) and uniformed primer pockets (~.05 grains). I kept track after each step. I then got 20 cases that weighhed the same at all stages of the process. So, I took the center of the normal distribution of cases that weighed the same at every step to .05 grains. I am going to shoot ten shot groups at 1000 yards with these and compare to the light and heavy to see if it makes a difference.

I have never really sorted cases by weight but if it makes a difference, this test should tell me. I hope it doesn't matter considering the expense and effort involved in doing this little test.


275.5 1
275.6
275.7 4
275.8 2
275.9 4
276.0 6
276.1 6
276.2 2
276.3 7
276.4 7
276.5 10
276.6 13
276.7 23
276.8 27
276.9 41
277.0 35
277.1 58
277.2 60
277.3 56
277.4 80
277.5 71
277.6 95
277.7 65
277.8 71
277.9 63
278.0 39
278.1 34
278.2 43
278.3 24
278.4 22
278.5 13
278.6 7
278.7 4
278.8 1
278.9 3
279.0
279.1 1
279.2
279.3
279.4
279.5
279.6
279.7
279.8
279.9 1
280.0 1
 
when reloading for my .308 i sort cases into lots that vary +0.01 to minus 0.01 . the separated lots seem to shoot better than just using cases that vary 1 to 2 grains. i don't seem to get as many verticals as i do with cases that are not sorted into lots. my velocity's are closer and my SD is lower. i would think this adds to accuracy. i may be wrong but in the last 30 something years, its made me feel better about my ammo. on my light guns ones with cases that hold less than 35 grains i sort to +0.01 and no minus. i have to go through a passel of brass to get enough sometimes but thats what im willing to do to try and eliminate my ammo as one of my problems.
 
I did an experiment several years ago to determine just how much effect brass weight has on .223 loads. I used WW brass (sized, trimmed and deburred, primer pockets uniformed, flash holes deburred, and neck turned) , WSR primers, charges of RL-15 or N-550 powder weighed to 0.1 gr, and 75 gr A-Max bullets. Using the lightest and heaviest cases (sorted from 1000 once-fired I had on hand), I had two lots of 10 cases with a 3 gr difference in weight. The average muzzle velocity difference was 16 fps, just a bit more than the 12 fps due to 0.1 gr of powder. I choose to sort 0.5 gr lots of brass for my long range loads, but the effect will only matter at 800-1000 yards - the vertical displacement on the target from such a small velocity change is negligible at shorter distances. Unless you control all other sources of variation, the effect of brass weight is negligible.
 
Doug. Good for you. I think you should throw out the first two rounds after a clean barrel, & I'm not sure I'd trust fireforming loads, but when you get the brass ready for record rounds, you'll be in great shape to decide if sorting brass is worth it to you.

I figure you're getting about 15 fps average difference between the lightest & heaviest cases. While that should be well within your tuning window, as long as you've sorted them it can't hurt.

The only thing I want to know is how you can afford 1,000 new RWS 8x68 cases. Too late now, but I guess I should have followed a different career.
 
Charles E said:
Doug. Good for you. I think you should throw out the first two rounds after a clean barrel, & I'm not sure I'd trust fireforming loads, but when you get the brass ready for record rounds, you'll be in great shape to decide if sorting brass is worth it to you.

I figure you're getting about 15 fps average difference between the lightest & heaviest cases. While that should be well within your tuning window, as long as you've sorted them it can't hurt.

The only thing I want to know is how you can afford 1,000 new RWS 8x68 cases. Too late now, but I guess I should have followed a different career.
Click to expand...

Charles,

Components seem to be constantly increasing in price so I decided to buy a lifetime supply of the brass all at once. RWS brass is not alway availables o having a bunch on the shelf is a plus. Also, I figured that if sorting by weight made a difference, I would have numerous sets of weight matched brass. If I decide it doesn't matter, I can always sell boxes of weight sorted brass for a small profit to those that do believe it matters.
 
I too find weighing cases to be a big waste of time and very misleading.

I used to do just that and thought all was well until I couldn't get a rifle to shoot. Mucked about with everything I could think of but it was always throwing flyers - seriously out of the group/four letter word type flyers.

Back at the bench for whatever reason, I looked into the freshly loaded cases and to my amazement, I could see a difference in powder height. That's alot of volume variation if you can see powder high and low.

Comparing that batch of brass, I found that CASE VOLUME varied substantially despite having identical case weights and other external measurements.

Case volume is a large component of case pressure which determines velocity and the variation of such.

It was a pretty neat thing for the light to go on. That batch of brass went into the trash and I started over.

This time I worked with fireformed brass that was prepped normally BUT with their volumes compared. The volumes were held as tight as I could measure.

Low and behold, my problem went away and groups shrank overall.

So now, after many hundred more cases in various cartridges, I compare volume not weight. That matters and is easily done by filling one case with a very fine gunpowder then dumping into another case. If there is a variation in case volume, the powder level with be higher or lower. Takes only a few minutes to compare 50 cases and I KNOW the volumes are the same.

The real proof to me was one day hand priming some 308 cases. Although all the cases were of the same volume, some would be tighter in the Lee shellholder. Weighing these cases showed that they were way off the weight norms of the other cases.

How important is the sizing of the extractor groove?

Certainly enough to influence cases sorted by weight but I bet it does diddly on the target.

Now the next hurdle is learning how to anneal properly so my neck tensions stay consistent.

Jerry

PS I stopped testing loads over a chronie looking for ES/SD numbers to determine vertical stringing. My Chronie, and all other chronies, have a mechanical error which is tied to the optical sensors and timers. Some are less then others of course. My Chronie comes from the factory with a note that it has an equipment error of 1/2% - which is pretty good actually.

So for a 3000fps reading, +/- 15fps is already built into the data. Trying to analyse data with that much built in error seems pointless to me.

I use the Chronie to let me know if I am getting to ambitious in my velocity and I use paper to determine my vertical. Seems to be working.
 
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Back at the bench for whatever reason, I looked into the freshly loaded cases and to my amazement, I could see a difference in powder height. That's alot of volume variation if you can see powder high and low.
Click to expand...

Well, maybe. How the charge of powder packs in the case will cause a variation in the "height" of the powder column. For example, some wonder how you can get 30+ grains of N-133 powder into a 6 PPC case. . . it is called a long drop tube & then dropping the charge slowly.

If you weigh charges & just dump them from the pan into the case, you will see a variation in how high the powder comes up the case, even if the cases have equal volume, unless your "dumping" procedures are exacting.

I always figure the long drive to the range with the cases being jiggled will settle things to about the same packing of the powder. Sort of like the machine we had in the lab when I was a research tech in college. But if you don't have that long drive, no jiggling.
 
Height of the powder??????????

I too find this a little hard to beleive. One grain in a ppc case maybe but I defy you to even notice one grain difference in height in a WSM case, etc. If there is a difference in height, wouldn't this be as a result of the web in the case, wouldn't it then weigh differently? Weighing cases is a short cut. Measuring volume via water is the only sure fire way to go. I personally don't go this far. But eyeballing different heights and then eyeballing the height of ball powder levels and comparing cases doesn't make much sense to me. But then what do I know???
 
You have both made valid points. As it turned out the fact that I saw a visual difference was enough to cause me to investigate which lead to my real problem.

maybe it was a fluke or a quirk of nature. Really doesn't matter now because it help me identify a real problem in my procedure and lead to a simple solution.

I much prefer the fine powder route (Win680 in my case) as there is no mess or error that can occur from errant moisture. Just pour to the brim of the first case, tap the case so that it compacts as much as possible, level with the case mouth, dump into the next case, tap, look, repeat till done. 50 cases can be tested in a few minutes.

You are looking for a comparative difference. If the height of powder is above or below the neck mouth by more then a bit, that case is suspect (using a funnel will catch any overages). Really doesn't matter what the total amount of powder is.

You are just using the same amount of powder (established in your first case) to compare all cases.

Simple...
Jerry
 
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Given fireformed brass............could someone please explain HOW brass cases could exhibit different volumes at the same weight?


al
 
alinwa said:
Given fireformed brass............could someone please explain HOW brass cases could exhibit different volumes at the same weight?


al
Click to expand...

two case may have the same weight, if the extraction grove is at a max tolerance, and the rim is at a max tolerance. if the case you are comparing it to, is at minimum tolerances in these areas and still weight the same. you could have a case with a large amount of internal difference.

so checking the volume with water is the scientific way of doing the check. but most folks can't check the volume in this manner due to not having the proper equipment to do so. just filling the case with water and weighing it will have the same probability for error as just weighing the cases. so we do the best we can with the tools we have.

i will admit that i have seen a difference in group sizes when testing weighed and sorted brass and testing unsorted brass. this will especially hold true for smaller cases where a small amount of added or lost weight can cause shot placement variations. as an example when i weighed my new .223 cases the lowest weight that i recorded was 90.6 grains the highest weight was 96.8 grains. given the high and low variance i would think there would be a difference in volume between the two cases.
 
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