Harold Ross made me a fitting threaded to take a 1/2" pipe compression fitting and threaded to fit into the hole on my reloading press.

I soldered on a Coleman funnel on top of the 1/2" copper pipe.

It works great.

Hole drilled through fitting with a tapered mouth to accept different diameter cases. 

Push case tight up against fitting with the press handle when dropping powder down the tube.

A very similar piece can be easily built using parts from a hardware store, if you don't have a lathe, or a friend with one!
My drop tube is a piece of hard drawn copper tubing, a compression fitting for tubing at one end, and adapters to fit into a plate I built. Used 1/2" pipe locknuts to clamp it to the plate and hold it. The compression tube fitting is drilled out, so the tube can slide through. This allows me to adjust the height, by sliding the tube up or down and snugging the fitting.
I also soldered a funnel in the top of the tube to pour easily.