Unfortunately, you're not going to find any RCBS progressive presses in stock anywhere and that is going to continue for many months to come - perhaps as long as nine months, according to my source at RCBS.

I don't know much about the Dillon 550 but my 650 will accept RCBS dies. You won't use the RCBS expansion die as Dillon's powder measure uses caliber-specific "funnels" that also expand the case mouth. And Dillon loaders are set up to seat the bullet and crimp the case in different stations but you could remove the seating stem from an RCBS die and use it for crimping only if you buy a Dillon seating die. Their dies come with a reversible seating plug that has a round-nose shape to one end and a flat-nose shape on the other. Or you could use an RCBS seating die and let it crimp as well. You would then just leave the loader's last station open.

You are smart to start with a progressive loader. Most of us began loading metallic cases with a single-stage machine and many of us still do but when time is of the essence or, like me, if the arthritis makes the rotational movement of operating a loader painful, a progressive is great. Back in the mid-1970s, I loaded 4,000 rounds of .38 Special wadcutter ammo for a local police department whose regular supplier couldn't meet the department's deadline using my RCBS RockChucker and one loading block. I loaded shells every night for a month and thought I would NEVER get done with those 80 boxes! I physically could not do that today (and am smart enough not to offer).

Dillon gear isn't cheap but you get the best warranty and great telephone support. The same is true of RCBS but they can't supply product right now. Owners of other brands of progressive loaders will offer information about their brands. Along with price and availability, be sure to compare warranties and support. Without good support behind it, even the best product is worthless.

Ed