Assuming it's the same thing as hammer follow, it's usually caused by a worn disconnector or hammer. The disconnector prevents the hammer from moving forward u

Assuming it's the same thing as hammer follow, it's usually caused by a worn disconnector or hammer. The disconnector prevents the hammer from moving forward until the trigger is pressed again (semi-auto) or the gun is in battery (full auto, closed bolt). I suspect open-bolt guns don't have one, but I've never looked at the trigger group of an open-bolt gun so can't be sure.