The Howell Automatic Rifle was an early attempt to convert the bolt action Enfield into a repeating rifle. It was not a particularly polished rifle, as can be clearly seen by the need for a face guard, handguard, and clumsy metal tube pistol grip. The action was operated by a simple long gas piston added to the side of the rifle, with a contoured cam at the end to move the bolt (the know having been removed).
It is notable that neither the Howell rifle nor its South African cousin the Reider used Bren gun magazines. The Lee receiver is too narrow for a Bren magazine to be practical. Instead, extended Lee magazines were used, similar to extended magazines used in trench fighting in World War I. The Charlton didn’t use Lee magazines, but instead specially made magazines based on the Bren.