As I recall, an unloaded Thompson has an loaded (30 round mag) weight similiar to a Garand. Add in the 100 round "C" drum, and the weight should be around 20 pounds or so, so a little lighter than a loaded Minimi. :P But the drums aren't worth it- too noisy, too bulky, too crud sensative, all the problems with the Beta drums. I think I'll stick to straight magazines and belts if needed.