I have two 550s. The second one was purchased by trading in a new 450 that I picked up for about half price. (guy read the instructions, too complicated, so he sold it) Yes, I feel rotten :cry: :wink:
I load mostly rifle type ammo (not straight wall) on my 550s. When I am in the groove, I can load 3-4 hundred rounds in an hour. This is with the primer tubes already loaded up. Some of my match loads are down to 100 an hour when I am trickling the powder.
A friend of mine shoots 38 super and 9mm. He a 650 for one of them and still has the old SD for the other. (doesn't have to change over now.) He loaded, on average, about 1800 rounds a week for a number of years. He said the 650 is a little faster than his SD because of the hopper and a few other details. He said he can still knock out over 500 rounds an hour on the SD.
You will not be disappointed with either. The 550 will load rifle, the SD will not. The SD is faster, and with a little practice, can knock out 500+ in an hour. If you load a lot, this may be the way to go. If you just load a little, and may pick up a rifle, get the 550.
Steve
p.s. I bought the spare parts about 10 years ago. I might even open the bag some day if I ever need anything out of it!! (10k rounds a year average thru my 2 550s.) Two minor mistakes (tool head pins) and Mike Dillon sent out free parts same day. :grin: :lol: