Been a while since I read the book but that total weight of fifty pounds for gun and drum sticks in my mind.
The new guns with 16” barrels weigh in at 13lbs. with 50 rd drum. I don’t think 50 rounds of .45 weighs 35 lbs...so 50 lbs is way high. I’m putting the 12” barrel versions with a 50 rds loaded mag in the 15 lbs range
“Been a while since I read the book but that total weight of fifty pounds for gun and drum sticks in my mind.”
It’s possible someone handed SkyDancer a miserably edited piece of text.
No Thompson gun has ever weighed more than about 16 pounds, not in any configuration, not even when fully loaded. Browning’s Automatic Rifle M1918 weighed about 16 pounds; the M1919 belt-fed machine gun (also a Browning design) weighed less than 50 pounds.
The Thompson was the only submachine gun of US design with any history of development and series manufacture, at that moment when the United States found itself dumped without ceremony into WWII. Several had been patented or were in development (look up the Reising, UD M42, and US M2) but none showed sufficient promise over the Thompson to justify production in quantity.
Some 1,200,000 Thompsons did get made, mostly by Savage, during WWII, in the M1 and M1A1 variants: redesigns to save money on manufacturing. Very much old school (forged/machined steel, walnut), it was still costly (47 dollars per gun, compared to 26 dollars per US M1 rifle. Figures from the Museum of the National Armory at Springfield, MA).
Drum magazines were dropped for a number of reasons: apart from their heavy loaded weight, they were complex (hence costly), fragile compared to box (stick) magazines, less reliable than box magazines, and terribly fussy to load (partial disassembly required). Worst of all, they rattled when loaded ... not something desired by a commando sneaking up on the enemy.
The M3, developed at Aberdeen Probing Ground and produced by GM, was the first “modern” gun to see service with the US military. Stamped sheet metal frame, many simple - crude - parts made on simpler production machinery, much less need for costly finishing or involved fitting. Many do consider its magazine to be a step backward: single position feed compared to the Thompson’s dual position feed. The argument has never been completely settled: Britain’s STEn used single position feed and was cursed by most users. Germany’s MP-38 and MP-40 used single position feed and turned out to be perfect gems of reliability.
(It’s worth noting that since the Second World War, no submachine gun has relied on single position feed.)
The M3 was handier, lighter, and less costly than the Thompson. Many went to allied nations after the war, but some hung on for issue to vehicle crews and such until after Gulf War I.