Turns out I waited til Saturday to test out the Korean drum (life happens). It ran ok until about 15 rounds left and it ran out of umph. Maybe I didn't wind it up enough, dunno. The instructions said not to over tighten it so it's possible. I opened it and checked it then after closing, I wound it up and it finished fine.
I really like it but man, you can go through ammo quickly. With the dot and the drum, you can do some serious precision damage.