If you are locking the stop block down tight there is no way it can trim deeper than the case length it is set for. Remember, there are two set screws to tighten, one that locks the block in place and the other for fine tuning. I never used the little one, as I would trim a case to the proper length and then use it as a model to set the trimmer the next time. I used one of these for years, until I bent the shaft using a drill to trim a bunch of brass that was changing from one cartridge to a different one, with no trouble at all. I think you need to read the instructions that came with the unit or find some on-line.