I would say the these drop measuring procedures would be correct, but you said in your first post that there is a slight curve upward to the muzzles. Someone might want to correct me if I am wrong, but not all barrels bend upward. If I remember correctly, the Model 21s made prior to 1960 had a slight downward bend which made them shoot "dead on". This was changed in 1960. I don't know how many other makes were made in this manner other than the 21s. But I think the earlier 21s were.