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Hating the Digital Scale. After reading the comments here, I get it – digital scales won’t give you the same number twice. That’s a problem. What can we do to get more consistent measurements? Time for some experimentation and analysis.
Amazon now offers cheap milligram scales (https://www.amazon.com/dp/B071GYVQF3) - are they any good for reloading? For $18 delivered, this is the cheapest entertainment I've found in a long time. The label says "HomGeek" but the inexpensive load cell and electronics are likely found in many different models. I will admit that learning to use ± 1 milligram precision is a bit twitchy, but the warts become immediately apparent.
Demystifying the Digital Scale. A digital scale has four parts. 1) A Load Cell measures force (weight), producing a voltage. 2) Electronics stabilizes and amplifies the voltage. 3) The voltage is converted to a number. 4) Software converts the number and displays a weight.
Auto-zero. This is the worst misfeature ever for the reloader. It masks all other problems. I have never seen the “HomGeek” display anything within 13 milligrams of zero. Instead, it automatically remembers a random offset number, subtracts it, and displays “0.000 g”. If you don’t mind being off by 0.2 grains, then auto-zero is the feature for you! To work around auto-zero, I add a small weight (<1.0 gram) to ensure the scale stays away from the “dead zone”, at least until the other problems are identified and corrected.
Grains or Grams? This scale advertises 50.000g ± 0.001. That’s at least 50,000 counts - for any computer nerds, that’s 16 bits (65536 counts) of precision. The scale displays milligrams, grains, carats, and a few others. In a cheap digital scale, Software converts the number from the A/D Converter. Roundoff error is inevitable. The “native language” of a Load Cell is most-likely the finest measurement offered – in this case, milligrams. To work around the roundoff, I chose “grams”.
Load Cell Pre-Stress. A load cell is a piezo (quartz) crystal that produces a voltage in reaction to stress (weight) placed on the crystal. First, I placed a small piece of 110-weight card stock on the sample tray to act as a “shock absorber” – we want to “settle” the load cell, not annihilate it. I then lightly “bump” the cartridge brass (or powder pan) until the number stops moving, within 0.001g. I have observed the weight “settle in” (monotonically increase or decrease) after a change in load. Only then do I trust the number being displayed. After that, I press “Tare” and add powder to primed brass.
Drafts. Breathe on this scale, and it can register 10 milligrams. Close the doors, air vents, use a draft enclosure, etc. I learned to hold my breath when measuring, just like when squeezing the trigger. If the powder drop seems way off, dump the powder, re-zero, and try again. It’s better than touching off a hot load at the range because you forgot to press the “Tare” button.
Range Experiment. How do we know we are controlling powder weight? Are the speeds consistent? What are the other variables? For this experiment, I also weighed projectiles and brass within 1%, and powder within 1 milligram. (This level of OCD is not normal. Before retiring, I designed electronics production line tests.)
The test round is a clone (range fodder) for one of my personal defense rounds, a 9mm 124gr Speer Gold Dot. I chose 9mm because it is a high-pressure round, and the speed-vs-powder curve goes asymptotic at the high end – that is to say, it’s “twitchy”. Controlling the powder weight is critical to consistent speed. For reference, I used a few commercial Gold Dot rounds which are currently un-obtainium. It's OK – I now have plenty of reloads that are better than commercial.
Test Results.
I have also done the same load development and comparisons with Federal HST – both 9mm 147gr and .40S&W 180gr. Same results. While commercial Federal HST has lower standard deviation that Speer Gold Dot, the tightly-controlled reloads perform more consistently (lower standard deviation) than commercial ammunition.
Conclusion. This process, while over-the-top OCD, yields more-consistent ammunition than commercial vendors. Powder can be reliably weighed on a cheap digital scale to the nearest milligram, given some patience and a willingness to find the root cause of various measurement errors.
Caution: Before using a digital scale for reloading powder, it must report the same weight every time.
Amazon now offers cheap milligram scales (https://www.amazon.com/dp/B071GYVQF3) - are they any good for reloading? For $18 delivered, this is the cheapest entertainment I've found in a long time. The label says "HomGeek" but the inexpensive load cell and electronics are likely found in many different models. I will admit that learning to use ± 1 milligram precision is a bit twitchy, but the warts become immediately apparent.
Demystifying the Digital Scale. A digital scale has four parts. 1) A Load Cell measures force (weight), producing a voltage. 2) Electronics stabilizes and amplifies the voltage. 3) The voltage is converted to a number. 4) Software converts the number and displays a weight.
Auto-zero. This is the worst misfeature ever for the reloader. It masks all other problems. I have never seen the “HomGeek” display anything within 13 milligrams of zero. Instead, it automatically remembers a random offset number, subtracts it, and displays “0.000 g”. If you don’t mind being off by 0.2 grains, then auto-zero is the feature for you! To work around auto-zero, I add a small weight (<1.0 gram) to ensure the scale stays away from the “dead zone”, at least until the other problems are identified and corrected.
Grains or Grams? This scale advertises 50.000g ± 0.001. That’s at least 50,000 counts - for any computer nerds, that’s 16 bits (65536 counts) of precision. The scale displays milligrams, grains, carats, and a few others. In a cheap digital scale, Software converts the number from the A/D Converter. Roundoff error is inevitable. The “native language” of a Load Cell is most-likely the finest measurement offered – in this case, milligrams. To work around the roundoff, I chose “grams”.
Load Cell Pre-Stress. A load cell is a piezo (quartz) crystal that produces a voltage in reaction to stress (weight) placed on the crystal. First, I placed a small piece of 110-weight card stock on the sample tray to act as a “shock absorber” – we want to “settle” the load cell, not annihilate it. I then lightly “bump” the cartridge brass (or powder pan) until the number stops moving, within 0.001g. I have observed the weight “settle in” (monotonically increase or decrease) after a change in load. Only then do I trust the number being displayed. After that, I press “Tare” and add powder to primed brass.
Drafts. Breathe on this scale, and it can register 10 milligrams. Close the doors, air vents, use a draft enclosure, etc. I learned to hold my breath when measuring, just like when squeezing the trigger. If the powder drop seems way off, dump the powder, re-zero, and try again. It’s better than touching off a hot load at the range because you forgot to press the “Tare” button.
Range Experiment. How do we know we are controlling powder weight? Are the speeds consistent? What are the other variables? For this experiment, I also weighed projectiles and brass within 1%, and powder within 1 milligram. (This level of OCD is not normal. Before retiring, I designed electronics production line tests.)
The test round is a clone (range fodder) for one of my personal defense rounds, a 9mm 124gr Speer Gold Dot. I chose 9mm because it is a high-pressure round, and the speed-vs-powder curve goes asymptotic at the high end – that is to say, it’s “twitchy”. Controlling the powder weight is critical to consistent speed. For reference, I used a few commercial Gold Dot rounds which are currently un-obtainium. It's OK – I now have plenty of reloads that are better than commercial.
Test Results.
Code:
Avg Speed (fps) / Std Dev G26(3.5”) G19(4”) G22(4.5” KKM .40/9mm)
Commercial Gold Dot 1132/36 1157/25
Reloaded Gold Dot Pulls 1107/22 1114/14 1135/14I have also done the same load development and comparisons with Federal HST – both 9mm 147gr and .40S&W 180gr. Same results. While commercial Federal HST has lower standard deviation that Speer Gold Dot, the tightly-controlled reloads perform more consistently (lower standard deviation) than commercial ammunition.
Conclusion. This process, while over-the-top OCD, yields more-consistent ammunition than commercial vendors. Powder can be reliably weighed on a cheap digital scale to the nearest milligram, given some patience and a willingness to find the root cause of various measurement errors.
Caution: Before using a digital scale for reloading powder, it must report the same weight every time.
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