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Topic Closedcase weight differences

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Gunrunner View Drop Down
.416 Rigby
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** Forest Grump **

Joined: 05 July 2004
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Direct Link To This Post Topic: case weight differences
    Posted: 22 July 2004 at 14:12

   When loading for rifles I weigh all the cases I will use and separate them by weight.  Same brand of case, just different weight.  I know that the heavier cases will hold less powder than the lighter ones, if you want to keep pressure levels about the same.  

   Someone once told me that once you find a powder charge that works for you, to keep a record of the brass weight.   Thereafter, if you load in brass that is heavier or lighter to either add or reduce the powder charge by 1/10th grain for each 1 grain of brass weight. 

   In other words, if I load some 308 brass that weighs 160 grains each,  and the load is what I want, then later I go to load some 308 in cases that weigh 165 grains, I need to reduce the powder by .5 grains.  (5 grain heavier case, .5 grain less powder).

   I have used this formula in 308 and it's worked pretty well, in my limited tests of it.   But what about other cases?  A 223 is a lot smaller, and a 270 or 300mag is a lot larger. 

   Anyone have experience with this stuff?   Are there any set formulas?   Or is it just trial and error kind of thing?

   My eyes are goin' buggy from lookin' at this computer. Gotta go reload some 308 and 223.  That'll make my eyes feel better.  

Somebody better call the Secret Service. Let 'em know there's an illegal alien in the White House...and it ain't the cook!!
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waksupi View Drop Down
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aka Keeper of the Old Traditions

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Direct Link To This Post Posted: 22 July 2004 at 16:34
Unless you are shooting benchrest or 1000 yard competition, don't worry about weighing the cases. When you buy cases, just buy a batch of the same lot at the same time. I've shot a lot of mixed brass, and the rifles just don't seem to care that much, for that matter. Those few grains could be due to trimming, primer hole, web thickness, head thickness variations (most likely). Don't sweat the petty things, and don't pet the sweaty things. For the average guy shooting, just use them with the same components. Most rifles shoot better than we can in the field.
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dakotasin View Drop Down
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Direct Link To This Post Posted: 22 July 2004 at 18:45

i never could get a definitive answer to this question myself, so i tested it myself on 3 different rifles.

in my 1000 yard rifle (308), i found that meticulous brass prep made more of a difference than weighing cases. in fact, weighing cases proved to be a waste of time.

in my 7 mag, weighing cases did make a difference, but again, meticulous brass prep made more of a difference. the difference it made was barely noticeable from the bench, and certainly would not be discernable under field conditions.

in the 223, weighing brass did make a difference. enough of a difference that it is worth the time for that rifle.

overall, i agree w/ waksupi in that weighing brass isn't worth the time or effort, especially for rifles that won't be seeing long range competition.

if you do decide to weigh brass, make sure to start from a clean slate. new brass, trimmed to length so that all the lengths are identical. deburr the flash holes, and uniform primer pockets. now you can be sure that you are playing w/ an even field. then weigh your cases, and make your own cut-offs.

more direct to answer your question, that formula you have may work for 308-ish cases, but like you noted, the formula can't be universal because the weight of cases for alltogether different cartridges will be a lot different, and a .1 change in powder charge will affect a 223 tons more than it would affect a 7 rem mag...

Hunting is not a matter of life or death; it is much more important than that.
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The_Mountaineer View Drop Down
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** West BY-GOD Virginian! **

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Direct Link To This Post Posted: 23 July 2004 at 02:28

Hmmm..........This topic always intrigues me.

To me, the only thing that weighing the brass does is give you an idea of the factory's consistency in manufacturing it.

I managed to dig up one of my files from a brass weighing experiment using Remington 22-250 new brass;

Findings are as such:

Mean weight:  153.7 grns.

Max weight:  155.3

Min weight:  151.7

Avg deviation from mean:  0.66

The avg deviation from mean, to me, will be the most significant indicator of brass consistency.  If I were to find avg deviation from mean for the same caliber but in Winchester brass to be 0.54, in Federal Brass to be 0.78, etc.  I could safely make the assumption that the Winchester brass is most consistent.  However, I haven't tested other brands to see which one is "best" in this sense.

As for weighing brass after they've been fired, I don't do it because of differences in the fouling, and cleaning compound in my tumbler are just two more factors that are impossible to calculate for.

In other words, I totally agree with waksupi!

Paritur pax bello - Peace is obtained by war.
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Gunrunner View Drop Down
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** Forest Grump **

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Direct Link To This Post Posted: 23 July 2004 at 05:14

   I think Dakotasin is right on the brass prep being more important than case weight.    I've been using Win brass and found that the cases are very close to each other.  The lot I have now is within 2 or 3 gs.  No way am I going to bother separating those. 

   On the other hand I have about 150 pieces of Fed 308 (once fired factory brass that a friend gave me) that weigh anywhere from 154 to 172 gs.  That's a big difference.  Not just a few that are light or heavy, but the whole batch.  So I separated them into 3 groups, each group being within 3 to 4 gs. 

   All this weighing was done after I had cleaned, trimmed, etc... 

   The lower weight cases are about the same as the Win I have, so I'll just use the same powder charge.  On the heavier ones I'll reduce the powder just a bit, run em over the chrono and see what happens. 

   If they turn out to be turkeys I'll just put them in my old brass box, take it all to the recycler, and get some more Winchester.    

Somebody better call the Secret Service. Let 'em know there's an illegal alien in the White House...and it ain't the cook!!
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