A method for operating a semi-automatic firearm as a single-shot firearm comprising: installing a hole in the firearm, wherein the bolt comprises a bolt lock safety device, wherein the bolt lock safety device extends beyond a face of the bolt when engaged preventing the firearm from automatically reloading; when the bolt lock safety device is engaged, pulling a charging handle back to cause the bolt to move rearward exposing the firearm chamber to reload a cartridge, wherein the adjustable bolt lock is simultaneously rotated by the lock pivot pin to lay flush with the bolt forcing the bolt back into forward position; and upon release of the charging handle, automatically reengaging the adjustable bolt lock via a lock return spring causing the adjustable bolt lock to extend beyond the face of the bolt.