On youtube there are Thompson SMGs being fired on the range chugging along at about 600 or so RPM.
In the movies it sounds more like an MG42 at 1250 RPM. BRAAAP like tearing cloth.
And Jason Robards didn’t look like Capone at all without wearing extra lips & some cotton in his face like Brando.
At least they got the cars right.
The first prototype Thompson had a higher rate of fire and it was purposely reduced. My brother has a 1921 and the 1928 models and a Youtube vid detailing the differences. https://www.youtube.com/watch?v=BsvWabSvi1I