The airgun with variable power, mentioned in last post, can be seen on plate 80 of Arne Hoff's "Airguns and other Pneumatic Arms" Although not a repeater it is standard looking butt reservoir airgun that has on the left side plate a lever. Hoff writes, "Left side of airgun, signed on the barrel 'Franceso Colle Ampezzo'. The pointer represents an internal device regulating the blast of air from N(ulla) over M(ulto) to T(utto) - Town hall of Cortina"
It seems to me that this lever is positioned to vary the upwards pressure of the latch spring.
I'll scan and post the picture tomorrow.