What movie? Looks like NY cops, vintage 1930's. I would love to have that 100 round Thompson drum.
Mike, the tear gas projectile was loaded in what looked like an oversize shotgun shell. The gun broke like a single barrel shotgun to load from the rear. Police still have them.
(It has to be a movie or a posed picture; in a real standoff, the photographer would not have been or allowed to be out front to take the picture.)