I modified the Powder Trickler by Nick van Noordwyk, to add a cap to the bottom. That made it easy to add some weight for stability.  Nick graciously provided his Fusion 360 project file, which made it super-easy to make changes to it.

The tube does not fit the holes made for it straight off the printer. No surprise there, really. I reamed out the holes by hand with a 27/64" bit, and then the tube fit right in very snug, but would still turn freely. The exact bit to use will depend on your printer.

After installing the tube, use a marker to mark a spot in the center of the tube inside the hopper.  Remove the tube, and drill a hole in that spot.  The size/shape of the hole will depend on what powder you're using. You can print multiple tubes for different powders, if necessary. I drilled a 4mm hole, which seems to work well for IMR4895 rifle powder.

I filled the base of the trickler with #8 bird shot, and attached the bottom cap with hot-melt glue. The extra weight gives the trickler good stability to operate it with one hand.