The plunger in the tip of the base pin pushes the transfer bar out and away from the firing pin.
The notches or "steps" on the hammer's face will block the transfer bar from moving up but not down as is the case when the trigger retracts.
All of this babble leads me to suspect your Hunter is suffering from "transfer bar pinch". The force of the mainspring is pushing the hammer against the transfer bar and not permitting the trigger return spring from pushing the trigger forward which also retracts the transfer bar.
So, on MY GUNS I've found a simple solution. First, a test. Unload gun. Check again that it's unloaded. Now cock the hammer and then dry fire and keep the trigger held to the rear. Now, carefully watch the hammer as you slowly let the trigger return to it's "at rest" position. As the transfer bar retracts down into the hammer well you'll probably see the hammer move forward slightly as it clears the "notch" on the hammer's face. On MY GUNS I've increased the depth of that notch so that the hammer does NOT move one bit as the transfer bar is retracted. A thousandth or two of clearance won't effect the firing pin's job since it's smacked really hard and has plenty of inertia to fire a cartridge. All parts are smoothed out in the interest of reducing friction. This procedure also stops "transfer bar" breakage due to dry firing the New Model Revolvers.
The above is MY THEORY and is provided here for Entertainment Purposes ONLY and IS NOT RECOMMENDED to be performed on any Ruger New Model revolver.
flatgate