The Stevens M620 was an improved version of John Moses Browning's earlier M520 series, primarily with a more refined receiver. The firearm was available in 12-, 16- and 20-gauge and offered in 26-, 28-, 30- and 32-inch barrel lengths. As with many other pump-action types, the M620 featured a five shell tubular magazine under the barrel assembly. Each individual shell was then introduced into the firing chamber via the operator manually actuating the pump-action slide. Production of the type spanned from 1927 to 1953. A version with raised matted ribbing was later introduced as the M621.
Externally, the M620 followed conventional design wisdom concerning shotguns. The stock was well-formed with an integral grip handle (both of wood), leading to the rectangular receiver. The barrel was mounted over the tubular magazine which was partially shrouded by the pump-action slide assembly. The trigger group was slung under the receiver in the usual way.
A "Trench Gun" version of the M620 existed for wartime military procurement (primarily for use in World War 2). This variant utilized a perforated heat shield across the top of the barrel to protect the firer's hand and fitted a bayonet mounting under the muzzle for close-quarters work while generally being issued with shortened barrels when compared to their full-length sporting brethren. Overall, however, these versions retained much of the appearance and quality of the peacetime versions. The "Riot Gun" variant was similar in scope though intended for security or guard purposes as opposed to direct enemy combat. These were fielded with shortened barrels for the role.