Its not the powder. I am using the Hornady Haps and they are .356. I loaded up some minor loads with Hornady XTP they are .355. I hade the same thing happen the bullets were loose in the case.
Did some checking and found out that Dillon uses the same expander F for 380, 9mm, and 38super/supercomp. When you adjust the expander down like you should for the swager, the expander goes to deep in the case and expands
it to where the bullet is loose. Lucky I was using the .356 haps and didn't have a problem, but when I went to the .355 xtp that is where it showed up. I had to pull 300 round and reload them. I backed out the expander and all was great.
I load on a 1050.