I recently started reloading again after a several year hiatus. I have an RCBS Rockchucker, but feel I will soon want to get a progressive. I will never load rifle shells, so I am considering the Dillon SD versus 550. Wondering if other than the auto indexing on the SD, there are other significant differences, or what others have experienced. My needs would be pistol calibers, no magnums, mostly cast bullets. Thanks.