I imagine what "scotty" says about covers it. I expect it's not too different than the problems on my Dillon loading .223.
1) Be sure your Dillon powder measure is set up according to directions: with the handle completely down, and the ram up, the little white block in the powder measure slide must be all the way against the back of the slide to ensure proper case charging.
2) Hold the handle in the full down position for a longer time than you do when reloading pistols. This will give the powder charge a chance to get through that tiny neck.
3) With the .204, which has an even tinier neck than the .223, you may end up having to go with a ball powder in order to load progressive. I couldn't pretend to give a suggestion here, since I don't load for .204, but I expect there are plenty of published loads.
A quick perusal of the Hodgdon site shows loads for many bullet weights using such ball powders as BLC-2 & H335. I've used these powders in .222 and .223 with success, along with Win 748, so I expect you'll have little trouble finding a satisfactory load.