Assuming the rounds have soft enough primers for the "slam fire" auto to work...That little hook prevents the hammer from riding the bolt home. In some cases it could make the gun go full auto, but it can also cause the gun to magically transform itself into a hand grenade by firing out of battery. Its a very poor method of converting to full auto - its completely unreliable (if it doesn't either go full auto or explode in your face, it will stop dead, hammer down on a live round.)