The Gemini-20: A Digital Scale for Light Powder Charges

The Gemini-20 by AWS is a precise digital scale with accuracy that works well for the lighter powder charges of pistol loads. This post describes the Gemini-20 scale.

But first, it is time for the annual winter waterfowl picture from ATOTT Headquarters. This year there are a few swans mixed in with the Canada honkers, a little variety for nature lovers. These are Trumpeter Swans, a species that became nearly extinct in the 1930s due to loss of habitat and overhunting. Their numbers now seem to be increasing, although it is said there are still only about 5,000 trumpeters in the Midwest. We see a number of them annually, but they do not nest in our area, preferring areas further north for that. The Trumpeter Swan is the largest of waterfowl, with a wingspan of nearly eight feet, and the big boys get along just fine with geese, to which they are closely related. The picture provides a nice comparison of sizes for the Trumpeter Swan and Canada Goose.

Trumpeter swans with Canada geese

Trumpeter swans with Canada geese

Using a Digital Scale for Weighing Powder Charges

I have had good results using digital scales for a long time, as have many scientists and technologists. Chemists and pharmacists have used them for a couple of generations and the digital will be the only type of weighing device used in today’s chemistry laboratories in industry or education.

Among reloaders, there are some who are reluctant to give up the older beam balances that they are accustomed to using and that they know give them reliable results. They are suspicious of the quality and accuracy of digital scales that cost less than their favorite beam balance.

Speed and convenience of use swings the scale, so to speak, in the direction of digitals for me, and there is little reason to be anxious about their operation because accuracy is easily checked with a standard weight set.  Good standard weight sets are sold by RCBS and AWS, among others.  The first picture shows two digital scales that have given me good service, the DS-750 sold by Frankford Arsenal, and the Gemini-20 by AWS which is available at a number of outlets.

Left:  DS-750 scale;  Right:  Gemini--20 Scale

Left: DS-750 scale; Right: Gemini–20 Scale

The DS-750 has a maximum capacity of about 750 grains (50 grams), enough for all sport shooting needs. It professes an accuracy of 0.1 grain and the digital readout shows weight to one decimal in grain mode. The DS-750 in the pic has a 2-gram weight on the pan and it shows a weight of 30.9 grains.

Grains of what, you say? Well, actually, grains of grain. An old definition of a weight of one pound was that it was equal to the weight of 7,000 grains of wheat. That is still the stated equivalence of a pound and the unit we call a grain. Standard weight sets are usually metric, so we need a conversion. One pound is equal to 453.6 grams. Dividing 7,000 grains by 453.6 grams we find that one gram is equal to 15.43 grains. Two grains would then be 30.86 grains, or, 30.9 grains rounded to one decimal, which is what the DS-750 shows. It is right on the money. If I remove the weight, the reading will quickly go to 00.0. If I then replace the weight it will quickly go back to 30.9 grains. In other words, the performance is repeatable, which is what one wants. It is also very stable, that is, the zero value or a weight value does not drift to some other value over time. Not all digital scales have good repeatability or stability, but the DS-750 has always been outstanding in this regard.
The DS-750 has served me well for powder charges weighing in the 20 – 70 grain range, the normal range for most rifle cartridge reloading. It responds well enough that it is possible to use a trickler to bring a light charge up to desired weight. Its sensitivity deteriorates below about 3 grains, however, and its accuracy of 0.1 grain is less than desired for light pistol charges.

The Gemini-20 Digital Scale

I recently found and purchased a Gemini-20 scale,  offered by American Weigh Scales (AWS) located in Norcross, Georgia. This company obviously gets along well with Chinese manufacturers because AWS offers about a million different models of digital scales covering all imaginable weighing needs.

The 20 in Gemini-20 comes from its recommended maximum weight measurement of 20 grams. Remembering our conversion factor, that max amount is equal to 309 grains. That will handle common reloading needs, unless you need to weigh cast bullets for the .45-70 or some other big-bore boomer. You will get a scale with higher capacity for that.

I was interested in using the Gemini-20 at the lower end of its weighing ability. Here, the big news is that the scale is accurate to 0.001 gram! Most inexpensive digitals claim accuracy to 0.01 grams, so we gain one decimal place when we use the Gemini-20. Talking grains, the 0.001 gram precision translates to 0.015 grains. Using the usual rounding rule, the Gemini-20 is then expected to weigh accurately to 0.02 grains, a considerable increase in precision over the inexpensive 0.01 gram scales. If the scale actually delivers this level of accuracy, then we can expect a weighed powder charge to be no more than 0.02 grains more or less than its actual weight.

The Gemini-20 with set of standard gram weights from E.H. Sargent Co.

The Gemini-20 with set of standard gram weights from E.H. Sargent Co. Maximum 20-gram weight on pan

I found that the Gemini-20 does indeed deliver this kind of accuracy. After calibration, which is accomplished with a 10-gram weight followed by a 20-gram weight, I weighed ten standard weights from my E. H. Sargent scientific set varying from 10 mg (.01 gram) to 20 grams. In grain mode, the Gemini-20 returned weights for this range with an average deviation of less than 0.02 grains. Several weights were within 0.01 grains of actual, as with the 1-gram weight shown on the Gemini in the first picture, and a couple were right on the money. One standard differed by 0.04 grams from actual. Weight readings and the zero position reading were always stable and repeatable.

The sensitivity of an inexpensive digital balance decreases as weights get smaller. For example, a 0.01 gram scale like the DS-750 will not give a reading if just a 0.01 gram (10 milligrams) standard is placed on the pan. It is not sensitive enough to know that anything has been added. The Gemini-20, however, returns a weight of 0.14 grains when a 10-mg standard is placed on the pan. This is within o.01 grains of actual weight and is a truly remarkable performance.

My Application

Obviously, the Gemini-20 performs with precision greater than needed for weighing rifle charges in the 30-60-grain range. However, when I load a small case like the .32 S&W for use in an old top-break revolver I want good performance in the 1.5 – 2.0-grain range to maintain safety. The Gemini-20 does a great job in meeting this need. Needless to say, it will work very well for all pistol charges in the 1.5 – 10-grain range.

A shortcoming of the Gemini-20 is the small size of the pan it comes with. It is a little hard to get a hold on it, but its capacity is large enough for pistol charges. The picture shows that it will hold more than 25 grains of Accurate No. 9, one of my favorite magnum

Gemini-20 with charge of Accurate No. 9 in pan

Gemini-20 with charge of Accurate No. 9 in pan

handgun powders. Twenty-five grains of A9 equates to about 15 grains of Unique, 11 grains of Red Dot, and 7.6 grains of Trail Boss. Thus, the pan will suffice for handgun loads with various powders up through the .44 Magnum and .45 Colt. For larger charges, a washer fitting the circular pan base of the scale could be attached to a larger plastic weighing boat, or some such, but I have not tried that because I don’t need it. I will continue to use the DS-750 for larger charges.

The accurate Gemini-20 is a great little scale.  The lower maximum weight range and the two-stage calibration process contribute to its fine performance.  What does all this precision cost, you ask? The AWS web site quotes a price of $64.95 but a check of today showed one, eligible for Amazon Prime shipping, for the princely sum of $22.85. What a bargain !!

The Gemini-20 scae with its attractive box

The Gemini-20 scae with its attractive box

This entry was posted in Personal History, Uncategorized and tagged , , . Bookmark the permalink.

Comments are closed.