I have an absolutely beautiful 12ga. Specialty Grade (1926) with the Hunter One Trigger. One problem with it though...it will fire singly, but not consecutively. Any know what could be the issue??
The one that I have seen that causes most problems is the side plate connecting screw. Sometimes 1/4 turn will be too much. That screw should be flush on the thread side (right) with the lock plate. If it is sticking out just a bit, back it off 1/2 turn and see if the trigger is then working. If the gun was taken apart, I have seen the top tang to trigger plate screw too tight also. That screw from the factory was "timed" to the gun meaning the slot was parallel to the barrels. Plus this screw has a tapered head to match the top tang. If still having problems the best person for the job is Jerry Andrews.
I deal a lot in smiths and can about do anything to them being repair or restoration. The one thing I will not touch is the one trigger. Parts are too scarce and my skill knowledge isn't close to those who can. Besides a light cleaning to remove years of grime I think you would find yourself ahead sending it to someone who knows these triggers such as Jerry Andrews.