I agree with others who have said that regardless of how you measure, by weight or by volume, the key is consistency.
Once you find the accurate load for your arm (which will probably be significantly less than the maximum load), the key to consistent accuracy is consistent measurement.
I like measuring by weight because the scale does not care whether the powder settles or gets packed in tighter as can happen with a volumetric measurement.
However, it is a pain in the butt to measure every charge when I'm making up 300 cartridges for all my guns for a competition.
I'm going to get a Lyman 55 powder measure and use that for making up my cartridges. It dispenses based on volume. But as it is a machine, if you operate it consistently you should get consistent drops out of it.