I use an adjustable measure to throw 'stricken' measures when working up a load. I then weigh what the measure throws when set at the 'best' load and record the weight. I then make up an antler or brass measure which throws that same amount of powder - by volume. I find an internal diameter no larger than about .450", to throw very consistant 'weights' of powder. The larger the 'bore',t he more variation, thrown load to thrown load.
You cannot trust the markings on any powder measure. They are approximations only and differ depending on the granulation of powder used. A given measure will usually throw a few grs. more 3F than 2F, but that depends on the particualr powder's specific gravity, moisture content, etc. How you pour the powder into the measure also can make a big difference in the amount of powder 'thrown'.
It is best to have a handloading powder scale so you can wiegh what your measure actually throws and record that amount. Lose a measure and you can check, then make a new one that throws the same amount. Variation as close as 1/2gr. high to low thrown measures of powder is practical with a measure as noted, not larger than .40" to .45" in inside diameter and whatever length it has to be.