I recently weighed 153 pieces of once-fired Remington 223 brass that had all been full-length resized, trimmed to length, deburred, primer pockets uniformed, and neck turned. Here is the resulting data:
- Average = 90.8 grains
- Standard Deviation = 0.71 grains
- Average Deviation = 0.53 grains (average of the absolute deviations of the data points from the mean … 0.53gr actually isn’t that bad)
- Variance = 0.51
- Extreme Spread = 4.0 grains
- Extreme Spread as % of total weight = 4% (this is significant)
All data was gathered using a RCBS ChargeMaster 1500 Powder Scale, which is accurate to +- 1/10 grain and was calibrated immediately prior to use.
For match grade ammo, I only use brass that is within 1% of each other in terms of weight. In this example 0.9 grains is roughly equivalent to 1% of the total weight (90.8/100 = 0.908). So for this distribution, I gathered all pieces that weighed between 90.2 and 91.1 and called them my “match brass”. I culled the brass on the extreme ends and will use them to setup my neck turning equipment, but probably won’t ever load them. I split the remaining brass into two groups: under 90.2 and over 91.1. It will be loaded for practice rounds or “foulers” … just not for matches.
I’ve found a very useful method to sort brass as you are weighing it. I use a plastic eggcrate louver (typically used to diffuse light and protect flourescent bulbs in commercial applications). I bought it from Lowes for a few dollars, and it works like a champ. I just put all of the brass that weighs the same (to 1/10 of the grain) in the same column. An added benefit is it pretty much makes a physical distribution chart for you when you are done.
For more info on weighing brass, check out this helpful blog post from Sinclair.