I would have thought a supposedly well engineered rifle like the Cyclone would have had a transfer port securing screw, as Ben Taylor seemed to think, as the transfer port part of the barrel is separate from the barrel itself and is only secured to the barrel by friction fit and two 'O' rings. Poor design in my opinion.
I've made damn sure the two barrel retaining grub screws are nice and tight.
The other thing I discovered is that the hammer spring adjuster port has a hexagon keyed adjuster inside as well as the slotted outer screw. There are two adjusters listed in the parts list, one for .22 and one for .177, which is what my rifle is, but only one shown on the diagram.