Here are some schematics of the fantastic double pull trigger Diana attached to its various DRP models in the 1930s, the models 27, 35, 45 and 58, followed by pics of an actual trigger block and piston.
First, here is the excellent description of this trigger system Larry Hannusch included in his article on the Dianas 45 (see elsewhere in this section):
It first involves a very unique piston that has a long probe at its tail rather than the traditional piston “bent”. Nearest the piston body at the base of this probe is a conical head that is tapered at the back and straight sided at the front. The trigger block itself pivots up and down on a rear crosspin, and is kept in the downward position by the use of a small compression spring placed at the top front of the trigger block. This trigger block also contains a small, cylindrical wedge within its center. This wedge is cut for trigger sear contact on its belly, and is driven forward by an additional compression spring within the body of the trigger block.
As the lever is pulled back to cock the gun, the piston probe eventually pushes back the wedge against its spring until the trigger sear engages it, thereby cocking the set trigger. As the underlever finishes its cocking stroke, the cone at the base of the piston probe slips past the true sear that is incorporated into the inside front edge of the pivoting trigger block that is being forced downward by the small upper spring. At this point, the piston is held in the rear firing position by the front edge of the pivoting trigger block awaiting the pull of the trigger. As the trigger is pulled, the small wedge flies forward under it’s own spring force, and is driven against the tapered cone of the piston probe. As the small wedge is no match for the solid piston in its path, the wedge’s kinetic energy is deflected upward into the pivoting trigger block, overcoming the downward push of its small upper spring, and the leading sear edge of the trigger block is momentarily driven upward, releasing the piston to fire the gun. There...that was easy!
It is really a brilliant and sturdy design. The trigger itself has two small screw adjustments on it to fine tune the trigger to the shooter’s preference. Without adjusting either setting, I measured the trigger pull, and it breaks crisply and consistently at 2¼ pounds. That is quite impressive for a prewar sporting airgun. As a side note, the gun can be “dry fired” by cocking the underlever until the first click is heard, but before the second click is achieved, and then lowering the lever slowly. When the trigger is pulled, the set trigger is released, giving the same trigger feel as a complete firing. It is a little bit of trouble, and for my time, I’d just as soon complete the full cocking stroke, and leave the tap in the open, upright position to cushion the piston’s sudden stop for dry fire practice.
Some more pics of a model 27 double pull trigger stripped down. With thanks to Rod letting me use these:
Let's not forget the Webley version of Diana's double pull trigger. It was imported to the UK when Webley & Scott copied the 1930s DRP Diana mod 45 as the blueprint for its new successor to the Webley Mk2 Service air rifle, the Webley Mk3, available from about 1947.
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