If you are still interested in modding:
In the drum itself, the only problem is that the bullets rub on the drum body, and the more you load into it, the more friction you get, resulting in the carrier binding in the drum. A spray-on lube takes care of that.
This is where the major problem is: as the bullets rise up to the feed lips, they have to change angle and work their way forward, resulting in more drag and resistance to the spring. As well, they have a tendency to stack up in the "neck" of the mag, and I found they would often jam, taking all the spring's tension off the top round. This would lead to poor feed angles as the bolt stripped the top round out of the mag.
I don't have any pics of the inside of the revamped version, but this shows how, with the use of a factory mag, the movement of the rounds remains fairly consistent with the rotation of the drum's carrier, as the feed lips are more in line with the curvature of the drum. The factory lips do not feed from underneath as the promag does, but from the side, allowing the rounds to maintain the same angle as when in the carrier, resulting in a smoother transition at the top.
Don't know if this helps, the promag is a frustrating product and I had to see if I could make it work better. Don't mind the beads of hot glue, it was a good way to hold everything together while testing, and easy to tear apart for fine-tuning. Also, as I said earlier, this particular butchery won't work on a 10/22 with a stock because of the way I set the factory body low on the drum. It works on my thompson, which was what I designed it for.