Here's a couple of tips from Lyman "Reloading and Cast Bullet Guide" that came with my 1990 Lyman reloading kit.
For coarse-grained powders Lyman suggests that you use all three slides together,whenever possible,to give you a narrow, deep opening rather than a wide, shallow one. The wide , shallow opening allows more powder granules to be lined up on the cutting edge of the measuring pocket. The reason is the coarse grains will be caught between the edge of the rotor and body of the measure, causing considerable resistance as the granules are cut.
All movements must be uniform-with the knocker operated the same number of times-when throwing each charge. Always keep the handle in down position except when throwing a powder charge.
I have two 55's an older 1990 model and a new model I purchased this year they both throw consistent powder charges. The 55 is my favorite powder measure. The new measures come with a baffle but I can't tell a difference with or without one,keeping hopper full helps also. I try to keep a good rhythm going when throwing charges and I have never had a problem. When using small fine power change I only use the the top slide. I have good results with the 55 even with 700X.With extruded tubular powders shaped like IMR 3031 I set up cylinders per Lyman's instructions and it works very well . For my rifle reloads I get measurements close with powder measure then finish with powder trickler for precise powder charges.