This is a Debris Catcher for Casefeeder for Dillon XL650 XL750. The Dillon Casefeeder has two holes in the bottom back of the bowl assembly. These holes allow any accumulated spent powder, polishing media or general crud to drain out of the bowl.
This debris if left unchecked can fall all over your press or bench top. Most reloaders just tape some kind of cup or even a couple of spent shell casings to the back of the feeder to collect the debris. This upgrade accomplishes the same thing in a more elegant manner.
The Debris Catcher is printed on a 3D Printer.