Which mechanical part on the firearm's action can impede the locking procedure on a blowback action?

The mechanical part on the firearm's action that can impede the locking procedure on a blowback action is the extractor. In blowback-operated firearms, the energy from the fired cartridge is used to cycle the action, and proper extraction is crucial for the smooth operation of the firearm.

The extractor is responsible for grabbing the spent cartridge case and pulling it out of the chamber after firing. If the extractor is malfunctioning or damaged, it may not grip the case properly, leading to failure to extract. This can prevent the action from properly cycling and can impede the locking procedure required for the firearm to function correctly. If the spent case does not come out smoothly, subsequent rounds may not be chambered properly, leading to potential jams or failures in the operation of the firearm.

Thus, the state of the extractor is critical to the successful operation of blowback actions, making it the correct answer regarding which part can impede the locking procedure.