I have both K&M Precision steel mandrels and 21st Century TiN mandrels in the exact same sizes. I was using the K&M mandrels which required me to every 10 cases or so put Umperial sizing lube on the mandrel as it would be much harder to pull through the case on the up stroke. I dont have to use any lube with the TiN mandrels, they are smooth as butter which is the main reason I switched. They both get the job done though, the TiN just save me time and hassle.
I tumble my brass in corn cob before processing it. I do not even deprime anymore. I have a Thumblers Tumbler B, Rebel 17 ss tumblers, and I have a ultrasonic and I have 2 dry media tumblers. I have done them all. I have done numerous testing and I have found zero advantage in accuracy or SD's SS tumbling, ultrasonic cleaning, depriming before tumbling, etc. Because of this I now throw my brass into the corn cob for an hour or 2, depriming and size all at the same time then throw them in corn cob again to remove the lube.