Ah, I see, okay.
Well, first step is finding the distance between the lands and bolt face. The RCBS kit provides what they call a "free bore tool" for checking max OAL from the bolt to the lands off the bullets ogive. For controlled feed rifles it works fairly well but, IMHO, it's no good at all for push feed rifles so I don't use that part at all.
I also have the Stoney Point max OAL and case measurement tools but don't really like them as well so I've reverted to the old way to find the max OAL. That's to close the bolton an empty chamber and run a cleaning rod (I actually use a wood dowel rod) until it hits the bolt face and lightly cut it, squarely, at the muzzle with a small knife blade. Then I remove the bolt and put the bullet I want to try into the throat, holding it lightly against the lands using a pencil as a "ram rod". Insert and mark the rod again at the muzzle. Using a dial caliper, I measure from knife mark to mark. It's quick, easy, cheap and plenty accurate for what is needed because I NEVER find best accuracy at or in the lands for factory rifles. Thus, it just becomes a reference point for seating tests, not a specific measurement correct within a thousant.
I seat THAT reference bullet into a dummy case to precisely match the OAL I just measured for it. Then THAT dummy round goes into the die box and gets used as a transfer gage for all further work with THAT bullet. After I measure it on the ogive with the Case Mic seating thimble, my test rounds are seated back in .005" steps, as gaged by the Mic, until I find the best shooting depth for that type of bullet.
The Mic is also great for rapidly checking shoulder length on fired and then resized cases. Using the fired shoulder length as a reference, just set the sizer so the shoulder gets moved back an average of .002". That much provides for an easy fit and long case life with very little stretching. Understand that brass sprimg-back at the shoulder will vary a little so we can't get it exactly the same on each case, we must use a workable average setback or go nuts diddling with the sizer!
So, for case measurements and seating depth gages, both the Stoney Point and RCBS Mic tools actually work fine. As you can tell, I (slightly) prefer the RCBS Mic tools over my Stoney Point tools. The RCBS length measurment thimble-tools are totally consistant between loading sessions and using them leaves my dial caliper free for other measurements.
On the other hand, I think RCBS charges much more for the Case Mics than can be justified (as is usual for RCBS). So, if I had to start over at today's prices I'd likely stick with the Hornady/Stoney Point or the simular style Sinclair tools and be comfortable with them too.