Been a while since anyone updated this, wanted to show some measurements I got from a few batches of BB's I had.
I utilized as closely as possible Raiths methodology of measuring the BB's. All measurements in MM.
Echo1 .25g BB's
1. 5.96 5.97 5.97
2. 5.97 5.95 5.96
3. 5.97 5.97 5.98
4. 5.96 5.96 5.97
5. 5.97 5.96 5.98
Averages:
1. 5.966 should be 5.967
2. 5.960
3. 5.966 should be 5.977
4. 5.963
5. 5.970
A. What's the precision of your calipers? I can almost guarantee it is NOT +/- .005mm like the sigfigs in your measurements indicate. To get measurements like that, you need to be using either the most expensive, best quality calipers (which are very rarely digital, fwiw), or a micrometer.
Also, one of your averages are a bit off... and one has a rounding error.
and... your statistical reduction can't have 4 sigfig accuracy when your data only had 3... raith's were a bit confusing on this, but his measurements actually had much greater precision than yours based on his measurements, so it's not quite as bad since his extra sig figs were in the 100,000ths place instead of the 1000ths.
So: a more correct reduction of your data, assuming your caliper is precise to +/- .005mm,
1. 5.97
2. 5.96
3. 5.98
4. 5.96
5. 5.97
Overall average: 5.97mm. Error of twice the stated tolerance.