I bought my 550B used and, until now, have only had to switch out primer setups. The other day I had to do a full teardown of the priming parts and have run into a problem. The original spring under the primer cup was rusty so I decided to replace it. I got everything into adjustment except the depth of seating the primer. I prefer to seat the primers just a tad below the base. After several attempts I'm almost flush. There must be an easier way but it is not addressed in the manual. How do you more experienced users make this adjustment?