An M9 pistol is not capable of automatic fire, in any form. The firing mechanism is not designed to fire a new round until the trigger is released and pulled again. That is, what is commonly called the "action" of the pistol needs the trigger to be pulled to release the firing pin after each round is fired.
Firing Pin Block
The part is the disconenctor.
The disconnector.
The Marlin 795 has a built-in feature that prevents the gun from firing without a magazine in place. Though, the modification to reverse this feature is very simple.
Part of the firing mechaism prevents the hammer from falling again until the trigger is released to reset it. Without it, you would have the possibility of firing more than one shot per pull of the trigger.
Possibly a broken firing pin.
No - have you checked that it is firing on all cylinders - Sounds like the engine is mis firing or not firing on all cylinders.
How to replace a firing pin from a Charles Daly 20-gauge semi automatic
1,6,5,4,3,2
firing pin block
not if it is capable of firing full automatic...................
Best left to a gunsmith.