Weight sorting cases... opinions solicited

[mikecr]

At some point, the shooter's laziness becomes the limiting factor in accuracy!

 

[Erik Cortina]

At some point, the shooter's laziness becomes the limiting factor in accuracy!

Sounds like you are avoiding the question! Perhaps too lazy to answer! ;D

 

[tripcrow]

Erik,
I did a box of 35 good twice fired in a fire-form barrel Lapua 6BR AI, full prepped cases that had a fired primer in them and were all ready for competition use. All cases were filled and measured at least twice because I had trouble with an air bubble maybe every tenth case. The cases, after being de-primed have a spread of .7g in weight, the water volume had a spread of .33g. That volume difference equates to a 10fps velocity spread when loaded with 31.5g Varget and a 105 Berger VLD. And that means if sighted in at 200 there is a built in max vertical spread of .16” @ 400yds, .54”@ 600yds., and 2.2”@ 1000yds in this box of brass. By culling out 7 cases and marking them for sighters the max vertical spread that can be caused by case volume is reduced to .09”@ 400yds., .32”@ 600yds., and 1.28”@ 1000yds. Those numbers are according to Quickload and Sierra.

It should be noted that you really should have a $250+ digital scale that can measure into the .02g range or so. Doing this with a +/- .1g scale is a waste of time. And I'd guess that is a big reason why the myth of weight sorting brass has lasted so long.

 

[Erik Cortina]

Thanks Bill, the sounds good, the problem is that is doesn't work exactly that way because there are many other things going on when you fire a case. If it was that easy then if you loaded the same case and fired it into a group you would have an ES/SD of zero?

I'm not saying that volume sorting doesn't make things more consistent, all I'm saying is that I don't believe the results are linear. I don't think weight sorting is a "Myth", but merely a less accurate way of culling out irregular brass.

I appreciate you're input, however, have you ever took a load and shot it just with weight sorted brass and then shot it again with volume sorted brass and found one to be more accurate the the other? That's the kind of results I'm lookin for, the ones that matter!

 

[johara1]

Erik, I went through this and found rim thickness and the size of the extractor groove to be the the factor. They seem to be a non critical tolerance,so i gave up on weight sorting. The things that have more effect are, seating depth and bullet release and the trimming and pointing. A guy that is a very good 1K shooter i think has it right shoot them at 300 and weed out the flyers and mark them and use for anything other than record targets.
There is nothing that really makes you look good as a hummer barrel.....jim

 

[tripcrow]

Erik,
Early this winter I was faced with making up over 500 cases for 5 different calibers all based on the 6BR. I had heard guys argue that case weight doesn't equal case volume. So always looking for the short cut I took the 2 heaviest and 2 lightest cases out of a couple hundred and did an H2O test on them. They came out linear and as one would expect that believed in weight sorting. Think it came out to 15FPS difference. Case closed, on to making brass.

But then other threads popped up where guys were pooh-poohing weight sorting. So to see if my earlier result were a fluke I did 10 cases then the box of 35 referred to above. Both of those tests showed next to no correlation between weight and volume. So my assumption based on those tests are that weight only correlates to volume with the cases at the extreme ends of the weight spectrum. And from reading others results, other brands and calibers are worse. The clincher for me is that I have yet to hear of anyone that went through the PITA of H2O measuring their cases come up with any conclusion other than that weight does not equal volume.

I do plan on testing volume sorted loads over the crony to see how close they run to what Quickload says. But we've already started the shooting season here and my guns aren't even ready for that. So it'll be a good while till I can get around to those crony test. Besides Mike has me wanting to do some crony tests on primers before any volume tests. But the first test I want to run in a simple test on the correlation between web thickness and volume that I'm having a tool made up for now. The web is where I'm guessing 3/4+ of the weight/volume discrepancy lays. And it'd be real nice not to have to play around with the hard to repeat H2O readings I get when water volume testing. Or having to have a fancy expensive scale.