There are several reasons you might want to outside neck turn, even if you don’t have a tight neck chamber. Probably the best reason is that neck turning is the “easy button” to producing excellent concentricity.
…We typically refer to bullet imbalance in terms of CG offset. CG (center of gravity) offset is where the center of gravity of the bullet is offset from the geometric axis or center line of the bullet. With CG offset, we have an unnatural condition where the bullet is forced to rotate about the geometric axis or center of form while inside the barrel. But a spinning projectile always wants to spin on its principal axis (center of gravity) when free to do so…