Ain't H 380 a ball powder? Drop tubes and vibrating do pretty good with stick powders, but not much with ball. You might gain a grain or two when you fireform the cases, though.
My Lee #2 shows a top of 53 grains.
Between brass variation, powder variation, and the general cussedness of life, you sometimes run into book loads that you just cannot duplicate at home. This may be one of those cases.