On the piece the breech was externally threaded and closed by a threaded cap which swung on a carrier pivoted on the right side of the gun. Firing was by friction tube inserted in an axial vent in the cap.

Internally the piece was of hexagonal section (the angles of the hexagon being rounded) throughout its length, ie there was no chamber. The hexagon, made with a uniform twist, formed the rifling.

The gun was designed to be used either as a breech-loader or as a muzzle-loader, possibly to satisfy diehard Officers, many of whom objected to breech-loading on principle. If used as a muzzle-loader the breech end was sealed by a copper disc with a central hole opposite the vent clamped in place by the breech cap. Tangent sights as used on other ML and RBL equipments were fitted.

Carriages resembled the current wooden field carriages for other service equipments. There is little doubt Whitworth pioneered the system later called QF for when he used the gun as a breech-loader he enclosed the propellant charge in a sheet iron cartridge case shaped to fit the hexagonal bore, thus effectively providing obturation. After firing it was extracted with a special tool. If used as a muzzle-loader the charge was enclosed in a cloth bag as with other ML guns. Projectiles were precisely shaped to fit the bore with negligible windage; a wad in rear ensured complete sealing. Whitworth pioneered the use of streamlined shot and shell, and demonstrated the significant increase in range obtainable.