## Re: Which brass: Lapua, Peterson , or Starline?

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Reply #24 –

so i re-did my weight experiment for hornady, win, and starline 6mm creed. 50 cases each. the hornady had an ES if 6.2 gr this time which over the 149.3 gr average is ~4.5% variance.

compare that to something like powder charge of .1 gr variance over 43gr, which is ~0.2% variance.

i’m not much of a metallurgist, but since all brass was resized and trimmed to length just before weighing. if external dimensions are identical... either the interior volume is indeed smaller on some cases or the density of the brass is different (or both).

i shoot enough that many different hornady cases continually mix through my process in the washer mainly. i might have to start doing some brass weight sorting, 4.5% variance seems way out of line to me. winchester extreme variance was just 3.4 and starline was 2.9.

even just grouping into 4 groups per 100 would drastically improve the extreme variance in any given sub group... might even show up on target, who knows

My original thought too was weight should be directly proportional to volume when the outside case dimension was the same.

I measured a few case externally and found things like variations in extraction groove diameters, rim thickness and case wall variations. I cut two non-complient samples lengthways with a hacksaw and measured the thickness at the flash hole which was different.

Though not very scientific, it explained to me that the correlation can be swayed by several different factors.

It also told me that internal shape can be slightly different from case to case but still have the same volume. That is where my conclusion was made that case/weight volume may be perfect but some cases possibly shoot different because of internal shape. But I'm not smart enough or good enough to prove it.

Thats why unless a case is totally unacceptable, every case gets a chance to prove itself at the range. And a few "heavies" have found themselves marked with a sharpie as a cold barrel round for hunting. Same charge, probably a little less volume, but same point of impact as round 2 & 3 with nearly same MV.

Nuff said going outside to shoot.

Later,

Randy