As an update - I finally pulled apart the remainder of the .357 rounds (after nearly 7 months) and checked them. In one the powder appeared to be clumped together, which reinforces my theory that the powder was contaminated by the case lube. I put together 25 more rounds with 17 grains of 2400 behind a 110 grain bullet, and this time used CCI primers. Hopefully I'll get a chance to try them out before long. I'm keeping the batches small until I get more confident.
I did get my powder measure where it will throw an accurage charge of 2400 with each throw. I think a big part of that was that I finally got the tube that screws into the bottom of the meaure from RCBS - I emailed them for a price and they send me one for free. I had it in my hand within a week of contacting them.