Abstract: Apparatuses for converting magazine-loaded weapons into low capacity weapons and apparatuses for locking magazine-loaded weapons are disclosed. The apparatuses may be loaded into the magazine well of a magazine-loaded weapon and may be reversible secured in place. Removal of the apparatuses requires a tool to disengage the apparatuses from the magazine well. The apparatuses may each include a body configured to be inserted into the magazine well of the firearm having a cross-sectional shape that corresponds to the interior cross-sectional shape of the magazine well, a securing mechanism in the body for securing the body within the magazine well, and a tool disjoined from the apparatus and the firearm and operable to engage the securing mechanism. The conversion apparatuses may include a seat in a fixed position on an upper portion of the body for receiving and positioning at least one cartridge of the firearm.