Three die set and the 550B

You are correct in that you will not use your expander die on the RL550B.

You can use a powder cop die on station 3; we prefer to seat at station 3 and seeparate crimp at station 4, but you are free to seat and crimp at the same time .

You do not flare bottleneck rifle cases. On those, the funnel in the powder measure is female;the case merely goes up into the funnel and pushes it up to activate the powder measure. The funnel only guides powder into the case. So if you aren't shooting a semi or full-auto, no reason to crimp most bottleneck rifle rounds.

You can use RCBS three die sets in an RL550B but you'll be much happier with Dillon dies. In order to use the RCBS dies you have to set them so the first one deprimes & primes (pnly) & the second stage sizes (where Dillon dies normally bell the cases & dump powder because, they're already sized during the priming stage). Then you have to bell the necks & dump the powder at stage three, set the bullet on top & then rotate the shell plate before you seat & crimp the bullet in the last stage. Not handy. Also trying to start cases into the non tapered RCBS sizing die is a PITA. With Dillon dies you size & deprime/prime in stage one, bell necks & dump powder at stage two, seat the bullet at stage three (without having to rotate the shell plate with a bullet balanced on top a case), & then crimp it (or not, in the case of the .45ACP) at stage four. I've replaced all my straight walled case dies with Dillon except my RCBS .357 dies & I'll buy Dillon dies before I use up all my loaded a.357 ammo again. Dillon dies cut loading time for straight walled cases by at least a third.

Oregunner

You can use RCBS three die sets in an RL550B but you'll be much happier with Dillon dies. In order to use the RCBS dies you have to set them so the first one deprimes & primes (pnly) & the second stage sizes (where Dillon dies normally bell the cases & dump powder because, they're already sized during the priming stage). Then you have to bell the necks & dump the powder at stage three, set the bullet on top & then rotate the shell plate before you seat & crimp the bullet in the last stage. Not handy. Also trying to start cases into the non tapered RCBS sizing die is a PITA. With Dillon dies you size & deprime/prime in stage one, bell necks & dump powder at stage two, seat the bullet at stage three (without having to rotate the shell plate with a bullet balanced on top a case), & then crimp it (or not, in the case of the .45ACP) at stage four. I've replaced all my straight walled case dies with Dillon except my RCBS .357 dies & I'll buy Dillon dies before I use up all my loaded a.357 ammo again. Dillon dies cut loading time for straight walled cases by at least a third.

Oregunner

I'll have to second Oregunner's recommendation for Dillon dies. They will load ammo that is very accurate and the ease at which you can clean the dies without losing the settings is a big plus. They are well worth buying!