It may surprise you to know that in the
dim and distant past I once fired a
Thompson sub machine gun.
During my initial training in the Naval
Air Service in 1943 a few days were
allotted to small arms use. This included
the standard navy rifle, throwing hand
grenades and firing a few rounds from
the Thompson. This had a round magazine
but think there was also a vertical one
available. It's been so long ago I can't
recall how it felt during firing.