I hefted a Thompson sub-machine gun at Cabelas one time. It weighed a ton and that was without the drum loaded.
Is that a Thompson that you have pictured above?
I carried a Thompson in the Nam for awhile. Real boat anchor but, damn, could it chop brush.
Then I found an M-3. A little lighter but it still chopped through brush like a hot knife through butter.
Went back to an M14 though as it worked just as well in heavy cover but could reach out and touch people a submachine gun couldn’t.