I would avoid the SDB for the simple reason it is somewhat a standalone system with it's proprietary dies. Honestly, you can't go wrong with the 550, 650, or Hornady LNL AP. All three are great presses. I prefer auto indexing, and thus the 650 or LNL. However, others prefer the manual indexing. At the end of the day it's all preference. All three of those presses are high quality with great customer service. I have never owned a 550 but learned on a friends; after that I went to a 650. A couple years ago I tried a LNL AP and ended up selling the 650 and keeping the Hornady. Nothing wrong with the Dillon, just liked the way Hornady did a couple things better (priming system, half-step indexing, powder measure). It's all minor and if someone told me I had to get rid of my Hornady and go back to a 650 that would be perfectly fine.

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Mark