The breach lock is for use in securing open the breach of an assault rifle during cleaning of the bolt action and the breach between uses of the assault rifle. The breach lock includes a notch along a top of the breach lock and a hole along the breach lock, which define a length. The breach lock is inserted between the upper receiver assembly and the lower receiver assembly so as to prevent any rotation there between. The notch bolts to the upper receiver assembly whereas the hole employs the pin of the assault rifle to engage the lower receiver assembly. The breach lock is simple in installation and removal with use of an assault rifle, and prevents unwanted collapse between the upper and lower receiver assemblies, which would otherwise pinch or injure the hand and fingers of an end user when cleaning.