A second tube right below the gas piston carried a recoil spring and guide rod, to return the piston forward after each shot.In addition, elements like two vertical pistol grips were added to allow more comfortable use from a bipod or from the hip, and cooling fins added to the barrel to aid its cooling (the original bolt-action rifle barrels are not intended for sustained fire).

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The bolt follows in the exact reverse of its opening motion, first being pulled forward and then rotating to lock with a new cartridge in the chamber.

In order to keep the cam plate stable, it runs in a groove in a metal plate attached to the left side of the receiver, as well as being fixed to the end of the gas piston.

The demonstration was received enthusiastically, and resulted in Field and Charlton being provided 10,000 rounds of .303 ammunition with which to further refine the gun.

Five months later, in November 1941, the pair returned to Trentham with the prototype (which now had well in excess of 10,000 rounds fired through it) and put on another very successful demonstration.

Field convinced him that ammunition availability would make that a non-starter for the military, and instead the pair decided t convert a Lee-Metford bolt action rifle into a light machine gun.

Such a weapon would use the standard .303 Army cartridge, and the New Zealand Home Guard had plenty of old Lee Metford and Long Lee rifles dating from 1889 to 1903 that could be subjected to such a conversion.They came away with a contract to convert 1500 Lee Metford and Long Lee rifles from the Home Guard armories.Manufacture In many ways, building the working prototype and getting military approval of it was the easy part for Charlton and Field.Charlton began by bringing into the project his friend Syd Morrison, who ran the Morrison Motor Mower company – whose business was struggling because of the gasoline rationing at the time.Morrison had the machine tools to do much of the work making parts for the Charlton, and it was in his shop that Charlton had done much of the work building his original gun.Now that they had their formal contract in hand, they had to figure out how to make the Charlton conversion into an efficient production job.