Re: Press advice please
All I have ever owned or used is an RL550B, since the early 1990's.
You <span style="font-style: italic">can</span> load precision ammunition on it.
First, you can work all the cartridges through a single station at a time, just like a non-progressive press.
Or, you can run them through in progressive mode, taking each newly charged case out of the powder station, checking/adjusting it, and returning it to the powder station to be advanced further through remainder of the progressive cycle.
That's the method I use for my match ammo. Basically, the powder charge is the main thing that can come through as a variable. The other stuff stays consistent until you change a die setup.
To ensure better consistency, the base plate should be adjusted snug, with just a smidge of drag.
The powder measure can be cranky about cylindrical powder kernels. Keeping the powder path clean helps, and static charges that can retard flow can be dealt with by providing the press with an electrical ground.
Because of static, I will sometimes postpone loading if the humidity is especially low.
Don't be concerned about the vertical play in the toolhead, it has no significant effect on accuracy.
Using the 550 can actually be an advantage, because of the interchangeable toolhead. It permits a die setup to be retained between loading sessions; so as long as the one session produced good ammo, it's highly likely that successive sessions will conform to the same spec until a die adjustment is changed.
Greg