Re: 7 WSM on Dillon 550 Xtra large powder die needed
The Powder funnel, cartridge specific specific shellplate and locator buttons are available for $42.95. For Exotic calibers, $51.95.
Powder dies are $9.95 each.
The magnum bar alone, for the powder measure assembly, is $26.95.
Tool heads are $19.95 each.
So if you are contemplating loading the 7mmWSM you'll need to provide the magnum powder bar for your measure, the cartridge specific funnel for an existing powder die (or an additional one), a tool head for your dies, and the correct shellplate and pins for the case head size (diameter). Most people have dedicated tool heads for specific calibers.
Many case heads are common so certain base plates can be used for other cases i.e., one size can be used for, .308, 30-06, .270, 8mm Mauser, .45 acp, 30-30, etc., with the same buttons. Others are red headed step children!
The various part numbers specific to individual cartridges are listed in the Dillon press manuals or the friendly sales people will walk you through it.
Sorry if you knew this already.