I heard or read the drum magazine was easy to break by overwinding it even a little bit.  The spring would spring without much effort.
Other than that, it's a cool looking weapon, that's for sure.  Be kinda neat to have a replica to hang in the "war room."  Was always more partial to the fore stock version, rather than the hand grip...(which looks gangsterish imo.)
First time I saw a full sized version (in a gun shop) I was surprized at the size, around 3 feet long!!!  That was one of the long barrel Thompsons.
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 If I absolutely needed a full auto sub gun for self defense purposes, I would choose a Mac-10.  No larger than a brick and weighs about the same.  That way I could carry it around with me. 
 
 Les