GT has written a good update, and has done ALL of the heavy lifting on this work!
I've helped with testing, a couple ideas, but mostly moral support and encouragement.
Like so many reproductions, if the manufacturer had taken just a little more care during construction these Numrich drums would have worked pretty good out of the box.
As it is or was done, there are lots of little and several big things that have to be re-done. I'm pretty sure no one since 1918 knows the innards of a trommel mag and what makes it tick like GT.
I can report for sure, there isn't much more fun to be had(standing up) than a 32 round drum being fired from a luger without a glitch.
No wonder they wanted it in the trenches in WWII!
Just another thought, if anyone has a problematic or broken original drum, many can be repaired or make to work using the same techniques.
So if you have tried your original and found problems, don't despair - contact GT for an assessment of the problem, be sure to give a good description of the problem(s).