Abstract: A dual use shell casing for use in a 9 mm firearm and for use in 9 mm magazines includes an upper portion, a lower portion, an internal cavity extending between the upper portion and the lower portion, the internal cavity configured to receive gunpowder and a projectile, and a tapered shoulder disposed at the upper portion and transitioning into a reduced diameter neck portion, the reduced diameter neck portion having an inner diameter equal to 0.313 inches. The tapered shoulder is configured to abut an internal shoulder within a barrel chamber of the 9 mm firearm.

Abstract: A combined firearm receiver and rail includes a handguard rail and a receiver housing disposed within the handguard rail. The handguard rail includes one of a takedown lug clearance slot, a handguard magazine port, a handguard continuous rail, a handguard ejection port, an attachment location, accessory attachment points, a handguard charging handle latch retaining slot, a charging handle housing, a charging handle guideway, a bolt catch clearance slot, a barrel cavity, a receiver cavity, an exhaust port, and a handguard section. In one variation, the handguard section does not come into physical contact with a barrel or a barrel nut of the firearm.

Abstract: A combined firearm receiver and rail includes a handguard rail and a receiver housing disposed within the handguard rail. The handguard rail includes one of a takedown lug clearance slot, a handguard magazine port, a handguard continuous rail, a handguard ejection port, an attachment location, accessory attachment points, a handguard charging handle latch retaining slot, a charging handle housing, a charging handle guideway, a bolt catch clearance slot, a barrel cavity, a receiver cavity, an exhaust port, and a handguard section. In one variation, the handguard section does not come into physical contact with a barrel or a barrel nut of the firearm.