I've seen metalbender's work in person, its pretty elaborate. Not going to speak for him, but making a drum mag work properly is a real pain in my experience. Obviously his skill and resources are advanced, I simply tried to improve on the Promag drum. I got mine to feed fairly reliably with a lot of chopping and trial and error (and some factory 10 rounder grafting).
My suggestion to all is this: abandon all hope ye who dream of a good, reliable (and economical) drum mag. It isn't worth the hassle or time unless you just really like to tinker. Ruger could make one with the same basic design as the factory mag (but expanded), but apparently they have no desire to do so. Live with the tried, tested, and true "banana" mags if you want more than 10 rounds, and get out and shoot your Rugers. The Devil has designed the .22 lr with a rimmed case, this is the biggest stumbling block in making a "cool" mag for the rimfire.
I have a Thompson 10/22, the drum mag now has a thick layer of dust on it.
That being said, if metalbender or someone else were to mass produce a good reliable drum mag....