Muzzle spigot outer diameter is 25mm. Rob Allen glass reinforced nylon muzzles are designed so that the primary band exerts its force along a line slightly below the rail, holding the spear in the rail on firing. Premade bands are easily inserted into the band holes by first fitting the wishbone through the band hole slot then pulling the band through the hole. The secondary band in the double muzzle pulls from the lower hole, thereby reducing barrel flex.

Both open and closed variations are available for the Rob Allen Speargun Muzzle. A clear line of sight on the open muzzle makes aiming much easier and far more accurate. This muzzle is significantly smaller in profile than conventional muzzles which makes it easier to maneuver as the drag has been dramatically reduced. Divers are able to view and track fast moving fish with ease.

An open muzzle allows for the spears to be held more closely to the line. Spear line can be led left or right over the open muzzle which ensures comfort for both left and right handed divers. Spears are much easier and quicker to load than conventional muzzles as they do not have to be threaded through an eye on the muzzle.