[Brad Deckard]

I have solved this.... I managed to get a manual dated 1953 and it mentions this lever in full with diagram. The lever was an addition added in about 1953, the manual states this is a new modification which is being fitted to bofors guns.
The lever is an indicator to tell the operators the condition of the breech. eg open or closed. it is not a mechanical pointer which moves as the gun is operated. It is a HAND OPERATED INDICATOR. when the guns breech is closed the indicator will be pointed at CLOSED. If by hand the operator trys to move the indicator over to point at OPEN it cannot be moved. ( the cam position inside stops the lever moving to the open position. Thus the operator knows the breech is CLOSED. If however the breech is OPEN , the pointer is still pointing at CLOSED.... BUT when the operator phisicaly moves the pointer towards OPEN, the lever will move across and can be held pointing to OPEN.. thus the operator knows the breech is OPEN. basically.. if the breech is open the lever can be moved, if its closed it cannot be moved. Thus the position of the breech is know without peering inside.