Weighing brass

[nodlenor]

When weighing your rifle brass, how much variation do you allow?

[wncchester]

Plus or minus what ever it takes to get 'em all in the same selection group.

[demigod]

Didn't we just cover this yesterday?

[Unclenick]

Yes. Here's a link to the thread with the answer to the question:

http://thefiringline.com/forums/showthread.php?t=434537

[nodlenor]

Thanks unclenick, I guess I missed that one yesterday.

[PawPaw]

Y'all weigh brass? I sort for headstamp and that's about it. I do weigh bullets when I'm bored.

[temmi]

+-.25g for cal 30 or over

+- .1g for 223

IMO there is no use weiging brass which has not been fully preped

[700cdl]

Match headstamps and trimming/preping so they measure to the same length. Weight isn't relative.

[nodlenor]

I've never weighed brass before but I've read that others do. I thought I'd try it just to see how much difference (if any) it makes. I wanted some guidelines on tolerances so I'd know where to start. I've weighed loaded rounds and have had some pretty wide variances but never checked to see how much difference it made in accuracy. I just thought I'd do some experimenting and see for myself.

[Unclenick]

I can tell you where precise weighing is interesting, if not necessary, and that is to help identify tooling. Brass is usually mixed after coming off the forming dies, and while you wouldn't expect the capacity differences to be any bigger than the weight, it is perfectly reasonable to expect some tool setups to produce more uniform brass than others.

I've done this two ways. One is to take a big piece of graph paper like the sign layout sheets that Walmart sells, and mark the bottom edge in 0.1 grain steps, then set each piece of brass over its weight, so the cases build up into a line. This results in a kind of histogram bar graph where the peaks represent the averages that came off each tool. I did that the last time I bought bulk .308 Winchester brass. I should have taken a picture, but the drawing below represents what I saw fairly well.



Another method I've used is to sample brass and record the weights in Excel and create a histogram in that program. Below is actual output from some Lapua .308 brass I bought and weighed 30 randomized samples of. Because Lapua is so much more consistent than most, I was able to feel reasonably confident that cases weighing 172.2 and below were from one set of tools and those weighing 172.3 and up were from another. It might not be right 100% of the time, but is right often enough that any tendency of the brass off one tool set to be better than the other can be detected.



You can select cases from the middle peak of these charts for match shooting on the premise that they are least likely to have an asymmetry due to brass stock weight or some other problem, but if you are doing that you will likely be better off to sort with a neck runout gauge. Below is a photo of neck wall runout sorting for some LC 72 .30-06 my dad has. These are sorted by neck wall runout in half thousandth steps. The column on the left had runout from zero to 1/2 thousandth as near as I could tell under the jitter noise on the dial indicator. The next column is 1/2-1.0 thousandth, the next is 1.0-1.5 thousandths, etc.

Since that runout shows up as bullet runout in loaded rounds, I set aside the best 30 for load development, where you want variables minimized. I bagged roughly the best 40% for prone slow fire prone and the worst 10% for standing off-hand, followed by the next worst 10% for sitting rapid and the remaining 10% for prone rapid. Most often it probably won't make more than a point or two or an X or two's difference in a match. But since there is spare time in winter and since it won't hurt anything to do it, I think it is good salve for the shooter's psychology.

[jake556]

I don't have enough time to do this i can get sub 1 MOA without doing this so I'm happy