. I don't believe modern powder measures that are properly used and cared for will throw wildly varying charges. Perfect charges every time? Regretfully, probably not. Charges with differences of a grain or two? I tend to doubt it. Having used mechanical powder measures from the utilitarian Lee powder scoop, up to excellent quality bench mounted precision micrometer equipped measures, I think every single one is quite capable of tossing a nearly perfect charge each time if used properly.
Still, we shooters hear stories of the dreaded 'double charge' that has dissembled a pistol (or rifle) in a dramatic and unfriendly way.
Does it actually happen? Yes, I think it does. While I suspect the lore might also include hand loaders who made serious mistakes with powder selection and handling, loading the wrong powder to the wrong charge, there is possible such a creature as the 'double charge'. It's cause, almost surely a distracted hand loader or poor procedures.
My cure is simple. No distractions, period. I don't reload with friends around usually, and if I do they are hand loaders as well and know when to shut up. In addition, very bright lighting over the bench, and a few simple procedures designed to catch a double charge. On the rare occasions I use my RCBS Ammomaster progressive press, I have a spot light aimed exactly where it will shine down into the charged case. I glance at every single case before I place a bullet into it. Anything with a funny load gets pulled out of sequence, and investigated. I've never found a double charge doing this, but I see no reason not to be careful.
Loading single stage, as I usually do, I throw all my charges as a set. Then, under the bright lights of the loading bench, I take a moment to carefully examine the charged cases. As the image above shows, a double charged case stands out like a sore thumb. This mornings loading included 9x19 practice ammunition with a light charge of fast powder. A double charge would have easily accepted a seated bullet, but would also have exceeded maximum charge with that powder.
Bright lighting, no distractions, and at least one dedicated examination of the charged cases. Simple measures to eliminate a very real danger.