by Seismic Sam on Thu Dec 03, 2009 8:00 pm
Alright, here goes my rant on electronic scales, and as a chemist I have used a variety of electronic balances for 34 years at 3M that were capable of weight precisions from 0.1 gram (1 decimal place) to .0001 grams (4 decimal places).
ALL of the reloading balances have a FUNDAMENTAL disconnect in grams versus grains accuracy, with the balances SUPPOSEDLY being good to 1/100th of a gram (2 decimal places) or 1/10th of a grain (1 decimal place). Well, people, that isn't mathematically possible. 1 gram equals 15.43 grains, so .1 gram equals 1.543 grains. and .01 gram equals .154 grains. So essentially, .01 gram is NOT equal to .1 grain, but instead .15 grain, which is 50% more than the rated accuracy of the scale. To get to true .1 grain accuracy, a scale would have to at least be accurate to .005 grams, or 2 1/2 decimal places, and there are NO electronic powder scales out there with this specification. So the spec of .01 gram / .1 grain is fundamentally flawed to begin with.
Now let's get into the fact that your are working with a digital versus analog scale. Beam balances that measure to .1 grain actually can be observed in their swinging back and forth to be dead nuts on the money, or a little high or low, or a full .1 grain off if you move the small counterweight, so if you push the envelope you can discern .05 grain differences if you want to. A digital balance, however, reads to .1 grains only, and as noted above it's doubtful if it's really capable of .1 grain accuracy instead of .15 grain accuracy.
Now, there are two situations that can occur with digital equipment, and these will be treated seperately, and for both of these we will assume that these balances are only capable of .15 grain accuracy, whic in my judgement is the actual case.
Situation #1: The "TRUE" weight is between two digital values that read .1 grain apart, but in reality this difference is .15 grains. The scale will fluctuate back and forth regularly between these two values, and if you know what you are looking at after using digital scales for 30+ years, you will realize that the actual weight is the average of the two values. So IF you know this, you can get the weight dead on by interpolating, but most of you will pick one of the points over the other, so you will be .075 grains off of the true weight, and you won't know if your number is high or low. This is the GOOD situation.
Situation #2: The "TRUE" weight is close to a single value, but it fluctuates up and down .1 grain while you are watching it. Cutting through the math, your accuracy is +/- .15 grains, so your total fluctuation is .3 grains on any given charge. In a max load situation, a .3 grain fluctuation with 231 or Bullseye is just plain unacceptable. If your load data is based on a low side digital benchmark, that scale could be weighing out a charge a full .3 grains higher than you think in some cases, which could get you hurt.
Now, if that isn't bad enough just based on the disconnect between .01 grams and .1 grains, plus the uncertainty of going from an analog measurement which you can observe quite closely, to a digital measurement where you have no idea what the microprocessor in the scale is actually doing with the data it is receiving, in reality the situation is far worse in real life. These scales are dreadfully suceptible to:
1. Temperature
2. Drafts
3. Electromagnetic interference, with the #1 culprit being flourescent lights.
All three of these can drive a cheap electronic scale absolutely bonkers, and you actually have to get on into a basement setting with flourescent lights and drafts (which would be common for most reloading locations) to watch what happens.
Finally, add to that that that your POWDER MEASURE may not be dropping the exact same weight every time, and couple that with the drafts and the lighting and the digital variations of a scale that can only discern .15 grain differences, and you have a total measurement clusterphque. You will be lucky if 1 in 4 of your digital weights are actually the right number.
I actually have a rather nice Mettler .001 gram three place balance that is quite stable and has the weighing pan shielded from drafts and the electronics are also shielded, and if you want to bring one of your cheap little plastic, unshielded balances out we can throw 50 charges of something like Retumbo or Herco where you will get packing variations, and then weigh the powder charges with both scales. I can guarantee you, the comparison will be uglier that me and HammAR put together. Seeing as I do load development work where I increase powder charges in .1 grain increments with a beam scale where I can tell if the charge is .05 grains high or low, going to a digital scale which could be off by .2 - .3 grains is simply not an option. My velocity data would be garbage, and there would be no point in loading up cartridges in the first place.
