I'm not sure if this is always true, but for me Bullseye powder, for whatever reason, can have some flakes stuck together in chunks.
When I'm using my Hornady bench powder measure it's usually not a problem. I can feel the mechanism cut through the chucks sometimes, but the cylinder where the powder falls into is large. Adjustments only make it more or less shallow.
Today on the press I was using a Lee Autodisk while loading 380 automatic. The disk I was using was only .34 cc which is a small hole.
When I use a progressive press I'm always very slow and attentive. Luckily I found a case that looked low to me. I measured it on my scale and it was only 0.8gr of powder. Not sure if that would squib or not, but it should have been 3.2gr.
I never found the chunk, but it's the only reasonable explanation. Does anyone else find this powder to be chunky and is there a method of sifting it to solve this problem?