2. ease of use in the field. straight walled cartridges have a small ability to clean themselves when they get inserted into the chamber. its why most people use a once fired cartridge case to clean out chambers when a special is used in a magnum..
Straight walled cartridges have more blow by. It's the thin necked 44-40, 38-40 bottlenecks that are left in the chamber for cleaning as they almost perfectly seal the action off.