An ammunition round (10a, 10b, 10c, 10d, 10e) for small arms or light firearm comprising: a projectile body having: first and second axially opposed ends (20, 18) and a cavity extending between the first end and the second end, the first end being a leading end of the projectile and closed, the cavity being capable of holding a quantity of propellant for propelling the projectile body; a plurality of seals (26a, 26b, 26c, 26d, 26e, 26f, 26g) extending about an outer surface of the body, each seal protruding radially from the body to form a substantial seal against an inner circumferential surface of the barrel, wherein a first and a second of the plurality of seals (26b, 26c; 26e, 26f) are mutually adjacent and spaced apart in a direction of a longitudinal axis of the body to form a seal bound outer surface portion of the body; and one or more holes formed in the body enabling fluid communication between the cavity and the seal bound outer surface portion of the body; characterized by: a boat tail portion located between an end of the seal bound outer surface portion of the body and the second end, the boat tail being tapered to reduce in outer diameter toward the second end; a tubular case sealed at one end by a base, the case fitted over a portion of the projectile body, and wherein the portion of the case extending across the seal bound outer surface portion is provided with a constant inner diameter; and where a spacing L between outer most points of two axially most spaced apart seals satisfies the relationship L ≥D, where D is the diameter of the maximum of diameter of the projectile body. a projectile body having: first and second axially opposed ends (20, 18) and a cavity extending between the first end and the second end, the first end being a leading end of the projectile and closed, the cavity being capable of holding a quantity of propellant for propelling the projectile body; a plurality of seals (26a, 26b, 26c, 26d, 26e, 26f, 26g) extending about an outer surface of the body, each seal protruding radially from the body to form a substantial seal against an inner circumferential surface of the barrel, wherein a first and a second of the plurality of seals (26b, 26c; 26e, 26f) are mutually adjacent and spaced apart in a direction of a longitudinal axis of the body to form a seal bound outer surface portion of the body; and one or more holes formed in the body enabling fluid communication between the cavity and the seal bound outer surface portion of the body; characterized by: a boat tail portion located between an end of the seal bound outer surface portion of the body and the second end, the boat tail being tapered to reduce in outer diameter toward the second end; a tubular case sealed at one end by a base, the case fitted over a portion of the projectile body, and wherein the portion of the case extending across the seal bound outer surface portion is provided with a constant inner diameter; and where a spacing L between outer most points of two axially most spaced apart seals satisfies the relationship L ≥D, where D is the diameter of the maximum of diameter of the projectile body. a boat tail portion located between an end of the seal bound outer surface portion of the body and the second end, the boat tail being tapered to reduce in outer diameter toward the second end; a tubular case sealed at one end by a base, the case fitted over a portion of the projectile body, and wherein the portion of the case extending across the seal bound outer surface portion is provided with a constant inner diameter; and where a spacing L between outer most points of two axially most spaced apart seals satisfies the relationship L ≥D, where D is the diameter of the maximum of diameter of the projectile body.