He tells me that he has used a Neil Jones volume measure for many years. He opens up a fresh 8lb Keg, arrives at his setting, checking against an Ainsworth scale; and used the keg over a two year period. Started in April, new BR season, and only opened it to transfer enough powder to load a 6PPC for two matches. About a hundred rounds worth of powder was poured out each time, and the measure was double checked against an Ainsworth scale each time from his air conditioned gunroom. October, about 3.5 to 4 pounds worth of powder, and the Ainsworth said the weight had dropped enough to require two more clicks on the measure to regain the weight loss. He had about four other cartridges/loads with different powders over a three year or so period require an adjustment. That is when he switched to buying a case or more from one lot of one pounders.
As an aside, most short range Br shooters cannot tell you what their 6PPC powder charge is, just what a good Culver, Harrel, or Jones measure setting # is. At the Super Shoot, I watched shooters fire a 5-shot group at 300yds that measured in the mid to low .2moa dumping from a measure. That's hide all five with a nickel accuracy.
If you are focused enough to weigh powder charges to one kernel of powder, should this be a concern to you?
My two kegs are full of RL-33, and I am using about an ice cream scoop full to load my 338 LAPUA.
Just kidding, I have two electronic scales, and about every 10th charge is weighed, often on both.
As another aside, every shipment, the powder companies "blend" the total. That helps keep the change to an insignificant amount to normal people.