The photo above is of a trigger module from a semiautomatic pistol. In the state of Massachusetts this is classified as a gun. All other parts or modules are considered just that – “parts” and “modules” and as such are not subject to registration laws in the state. What this means is that once you purchase and register the module shown you can build other guns around it using various parts and modules and the assembled guns are never registered. These are not “ghost guns” completed with parts from illicit sources, the parts and modules can be purchased from leading firearms manufacturers and retail gun stores without the need for any form of license or proof of age. They can be purchased at retail through the mail, across state lines. A trigger module from a 9mm handgun can be used to “build” a .40 caliber handgun or a .357 caliber handgun, neither of which will be registered or have the ability to be traced. 

The firearms industry concept of “modularization” has rendered the use of forensic ballistics to be null and void. A person can purchase a 9mm hand gun then purchase a complete .357 conversion module, drop the 9mm trigger module into that, commit a crime, remove the .357 module, toss it in the ocean, rejoin the 9mm trigger and slide modules and any bullet recovered from a crime scene could never be traced back to the owner’s original 9mm gun. The only record of the .357 module would be a sales receipt issued by whatever retailer, anywhere in the United States, sold the .357 module to the person who committed the crime.With thousands of retailers and dozens of manufacturers in the U.S. the task would be close to impossible. There is NO DATABASE for firearms modules or parts. 

The video below illustrates this process.