burbank jung said:
The difference is that a balance will give you the same result on the moon as it does on earth, while a scale will say the object has six times less weight, from which you might erroneously conclude the mass had got six times lower. The scale result varies with gravity, while the balance result does not because it uses the same masses as the counterweights. Normally, we compensate the scale using calibration weights, which works on earth, but if you went to the moon and tried to do that, the scale would give you a calibration error notice.
In general, loading and shooting are concerned with mass. Powder mass determines the pressure it will produce, which won't change on the moon. Bullet mass is needed to calculate momentum and kinetic energy and determine the reaction force the powder builds pressure against. On earth, gravity is consistent enough to generally use weight as a surrogate for mass as if it were the same thing. It varies about 0.7% with high values at the tops of mountains because, despite the increased distance from the center of the earth, the density of rock is higher than the average ground, so its gravity is greater. The low points are over deep parts of the ocean because water's density is lower than rock's (why rocks sink).
In the United States, though, the variation is only about 0.2%. That's an error of 0.1 grains of powder out of 50. So even if you dragged your scale up atop a major mountain without recalibrating it with a standard check weight, your powder charges would only be light by that much when you weighed them at a gravity low point.