eightbore,
The right shotbarrel trigger that also fires the rifle barrel is likely a single set trigger. To "set" it, push it forward until it "clicks" and then it will have a very light pull weight, some would call it a "hair trigger". If you try this, be sure the drilling is unloaded first, to try the trigger it doesn't need to be cocked. If it doesn't "click" and "hold" forward, it is likely out of adjustment. There should be a small screw behind the trigger. If the trigger won't "hold" when you push it forward(with some force), the screw has likely been turned in too far, sometime in the past trying to adjust the "unset" pull weight. This screw only affects the engagement of the sear in the trigger, itself, and will not adjust the unset pull weight. To adjust the "set" pull, back the screw out, until it will "hold" when pushed forward. Next turn it in, until it "trips" the trigger. Then turn it out 1/2 turn and it is adjusted. Additional fine adjustments can be made , either way, to suit the shooter. Once finally adjusted, you can put a drop of stock finish on the screw, to keep it from moving. This screw is very small, so do not use Loctite or epoxy. If the screw is missing, you will have some trouble buying a new one. If it is broken, you should send it to someone familiar with drillings. As Steve Meyer said earlier, you can make cases from 9.3x74R, but 7x65R will also work. The rim thickness may need to be adjusted. The correct bullet to use, should be determined by "slugging" the barrel.
Mike
