I just started using the RCBS automatic bench priming tool. Unit works great but I have noticed that it does NOT seat primers to the bottom of the primer cup. This is with both large and small primers. I can use my RCBS hand held primer and it will seat primers fully to the bottom of the cup. Anyone else experienced this problem? Suggestions? I've already tried different manufactures of shell holders, no help. RCBS no clue.

turn the case 90* and bump them again with firm even pressure.

Very surprised to hear this.

We have been using this tool for so many years, never had this or any other problems at all.

Mine works fine and I like being able to feel exactly what force is being put on the primer. Box it up along with some primed cases and send it to RCBS and see what they say.

Very good video of the RCBS auto priming tool in action. As you can see because the primer punch is cammed well up through the shell holder the primer without question has to be seated into the bottom of the primer pocket. In fact the video mentions that all primers were seated nicely below the case head. The only thing that could prevent this is the small spring on the priming rod or the primer holder sleeve itself being slightly too long and when the spring is compressed the primer rod cannot seat the primer deep enough i.e. the compressed spring is limiting the depth.

https://www.youtube.com/watch?v=S4nShKxk7Gs

I've found primer pocket crimp removal tool to resolve problems like what your seeing. Doing the crimp removal procedure on All brass, not just crimped, just plain eliminates any seating issues loaded on the 550b and sometimes with RCBS bench primer.

When I got mine I noticed what I thought was excessive play in the primer pivot feed and the handle. I took it apart and installed thin nylon shims which really tightened it up. While I had everything apart I lubed everything that slides or moves with tw25 grease. That included the sleeve and spring on the priming rams. The thing is tight & smooth now, works very well. It seems to work the best with RCBS shell holders. For primers not going in square on multiple shell holders I'd be suspicious of the machining where the shell holder snaps in. Measure it for square to the priming ram.