It all has to do with the triggering/sear system. Semi autos have a secondary sear system that makes it so you have to release the trigger and pull it again in order for it to fire again. Full autos have the secondary sear disengage when the bolt closes into battery and then seeing as the trigger is still being pressed, the gun fires and keeps firing until the trigger is released.
This is just the laymens term of full auto fire. I appologize that I didn't elaborate more into detail.
|