Just to correct a couple of misconceptions that I used to have too. All modern smokless powder is extruded as part of the manufacturing process. The powders most often referred to as extruded are stick or cylinder powder.
http://en.wikipedia.org/wiki/Smokeless_powder
Ball powders as a group are not any more sensitve to environmental variations than any other powders. Two of the most popular powders used by those who reload for benchrest competition are H-335 and Vihtavuori's 300 series. Both are ball powders and well appreciated for their consistency over a wide range of temerature and humidity.