I lost the case feeder shell adapter for my Dillon 1050 for .223 / 5.56 cartridges. I had been thing of doing this for sometime now and finally got to it. When I printed it, it has a nice snug fit to the press and the drop tube. I have a printed hole in the top rim for a timing pin. I did drill this out to 1/16" to insure the PLA wouldn't crack. You will need a 1/16" x 1/2" roll pin to keep the adapter from rotating like the original. McMaster Carr has them as well as the usual on line sources. They are $5.35 for a box of 250 so unless you plan on making a lot of these I would look around for a better source.
I printer vertically with supports. I had good bed adhesion in the area I was working and didn't have any problems.