MANUFACTURER – Sterling Armament Company Limited, Dagenham, Essex, England
STATUS – In service
SERVICE –British military, (as L34A1), Commonwealth, and commercial sales (as Mk 5)
During WWII, the Sterling Armament Company had been producing the DeLisle suppressed carbine along with its other projects. The DeLisle was a bolt-action weapon that used a very large suppressor to make a very quiet sniping weapon. A number of aspects of the DeLisle suppressor were incorporated in the design of a suppressed Sterling Mk 4 submachine gun.
Design of the suppressed submachinegun was begun by Patchett and others at Sterling in the early 1960s. The basic casing for both the receiver and suppressor for the weapon were made from a standard Sterling Mk 4 casing. The standard barrel of a Mk 4 was modified with six rows of twelve each small holes drilled into the body of the barrel. The holes display a spiral pattern as they are carefully placed to fit the grooved path of the rifling to minimize disruption of the passage of the bullets.
A part unique to the Sterling design is the diffuser tube that surrounds the ported barrel. The diffuser tube is almost double the diameter of the barrel and fits over it when assembled. The rear of the diffuser tube centers on a flange turned onto the base of the barrel. The front of the diffuser tube is partially closed with a threaded center hole. The center hole screws down onto the muzzle of the ported barrel, making it a single secured assembly. The front length of the diffuser tube has fourteen lengths of holes. Each length is either 12 or 10 holes with an addition set of 14 lengths of holes near the base of the diffuser tube, each length being either one or two holes. The holes were partially drilled through the body of the diffuser tube before being punched out to their final diameter. This makes the inside surface of the diffuser tube, the side facing the barrel itself, very rough, which assists the breakup of the propellant gas flow.
Surrounding the diffuser tube is a wrap made up of a number of layers of expanded metal mesh. The expanded metal wrap fills the space between the diffuser tube and the gun body of the weapon, which is covered by the usual seven alternating rows of 14mm (9/16 in) cooling holes, the rows being of either 9 or 10 holes each. Two bearing surfaces have been turned on the gun body, one at the front and one at the rear, of the cooling holes. The bearing surfaces are larger in diameter than the gun body. Sliding over the gun body and centering on the two bearing surfaces is the long suppressor casing.
The threaded muzzle of the ported barrel extends out from the first expansion body of the suppressor with the diffuser assembly. Over the end of the muzzle is screwed the front barrel support which secures the barrel and expansion body to the casing of the weapon. The front barrel support has eleven holes drilled through it spaced around the muzzle of the barrel. Six of the drilled holes are threaded to accept additional components. There is a key on an inside edge of the front barrel support that inserts into a keyway on the front of the gun body to maintain the alignment of the suppressor assembly with the casing of the weapon.
A deeply crowned barrel nut screws down on the muzzle of the ported barrel to prevent movement of any of the internal parts of the suppressor. Between two of the crowns of the front barrel support is inserted an Allen-head screw into one of the threaded holes in the front barrel support locking it in place and preventing any further rotation. Three long tie-rods insert and are threaded down into three of the other holes in the front barrel support. These tie-rods support the spiral diffuser assembly which fills a major portion of the suppressor. The spiral diffuser is made up of 16 disks, each with a split from the outside to a central hole and with three holes spaced along the inside of the circumference. The disks are spread and secured into a spiral by small lengths of tubing acting as washers on each of the three holes. Passing through the holes and securing the spiral disks and the washers spacing them out are the three tie-rods extending out from the front barrel support. The suppressor casing slides down over both the spiral diffuser assembly and the bearings on the gun body. The basic design of the spiral diffuser assembly is adopted from the original Delisle suppressed bolt-action carbine.
The ends of the tie-rods extend out from the spiral disk diffuser through an extension tube that acts as an additional expansion chamber. This extension tube seats over the front of the suppressor body. At the front of the extension tube is secured the front cap of the suppressor, which is held in place by three tie-rod nuts that screw down on the end of the tie-rods within the front of the suppressor body.
The complex assembly of the Sterling suppressor is considered by many military professionals to be one of the most efficient military sound suppressors available. The sound of the weapon firing is almost indistinguishable at only 46 m (50 yards) in front of the point of fire. The secure assembly of the suppressor also means that the weapon can be fired on full automatic without damage to the system, something that could only be done in emergency situations with the Sten Mk II(S) and Mk 6 weapons. The Sterling Mark 5 was adopted with slight changes as the Gun, Sub-machine, 9mm, L34A1 in January 1967. The lack of a front wooden handguard identifies the L34A1 from the commercial Mk 6. A black crackle finish can be found on both weapons as well as a smoother black coating.
