I am new to this forum but not to shooting and reloading. Being retired on a small fixed income it is time to save pennies! In my 71 years I have be OUT in back in shooting 3 times .... and this time is is more expensive!
Attached are 2 photos that may show you how I did this. I started with a PVC fitting with no threads in either end of the heavy duty coupling, $1.69 at Lowes. Almost any Hobby Shop will have brass K&S tubing. You will need 5/16 O.D. Inside diameter should be slightly more than 1/4". Find a 1/4" hex-head bolt ... My bolt is 1-1/2" long and the spring about the same. (I think Lowes also has springs in the specialty section). I am a pack rat so I had the "firm" spring that would thread onto the 1/4-20 threads on the bolt, and, the spring should be a "close fit" to the tube and still thread onto the bolt. I used some Lok-Tite to glue it to the bolt. Epoxy might work???
This sounds more complicated than it really is.
NOTE: The spring will "expand" as it is threaded on the bolt...... so it will have to be THINNED down with a grinder at the threads. (be gentle here). You may have some tight spots when turning bolt to "auger" the powder out the end. Inspect, and feel for rough edges, and lightly grind the area some more. When powder is put in, be sure you turn it the correct direction. If you don't it will not turn after a couple turns. (Just empty the contents and gently twist and pull out the bolt and spring).
PS. The brass tube gets a small hole drilled in it ..... and the bottom of the powder hopper is simply an index card, shaped to a close fit, and siliconed in place. Heavy washer was also siliconed onto the bottom as a base.
Photos should show enough to duplicate this ... and good luck.