Get yourself a Lee auto drum powder measure and enjoy consistent throws of whatever powder you want to use. I can consistently meter clays, 700x, e3, and any other powder I choose less than 3 grains no problem.
I use to struggle with the discs too until this measure came out. The big difference is the size of the cavities the powder is dropping into. With the discs you are dropping powder into a smaller diameter, deeper hole, making powder bridging much more likely. The auto drum uses a much larger diameter hole that you can make shallow for small throws, plus the powder is dropping down into the hole at a slight angle making it almost impossible for the powder to bridge up and throw a squib.
This is the best thing Lee has done for the world of reloading in years. Added bonus, it's cheap, about $35 from Titan reloading, and you can screw the measure into the powder threw die you already have.