What Is a Polymer 90 ‘Ghost Gun’ Kit?
Delve into the specifics of Polymer 90 firearm kits, from the "80 percent" receiver concept to the complex and evolving regulations governing their assembly.
The term “Polymer 90” is a common misinterpretation of “Polymer80” or “P80,” a brand known for kits containing a partially completed firearm component called an 80% receiver or frame. These kits allow an individual to privately manufacture a functional firearm at home. They provide the basic structure and sometimes the tools needed for completion, forming the foundation of what are often called “ghost guns.”
Understanding the “80 Percent” Concept
The central component of these kits is the “80 percent” receiver or, in the case of a pistol, the frame. Under federal law, the receiver or frame is the part of the weapon that is legally identified and regulated as the “firearm” itself because it houses the firing mechanism. An 80% receiver is a piece of polymer, or sometimes aluminum, that has been manufactured to a point just short of meeting the legal definition of a firearm receiver.
Manufacturers complete most of the complex shaping but leave specific, defined areas unfinished. For a pistol frame, this means the central cavity where the trigger group sits is not fully milled out, and the pinholes for these components are not drilled. Because these final machining steps have not been performed, the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) historically did not classify these items as firearms. This allowed them to be sold without the background checks or serial numbers required for completed guns.
The “80 percent” figure itself is more of a marketing term than a precise manufacturing metric, suggesting a buyer only needs to complete the final 20 percent of the work. The work required varies by kit, but the principle remains the same: the object is sold in a state that is not “readily convertible” into a firing weapon without additional machining.
The Assembly Process
Transforming an 80% receiver into a finished firearm component involves specific machining steps. Kits typically include a plastic jig, a template that holds the receiver securely and guides the user’s tools. This jig has indicators showing precisely where to drill holes and remove material, minimizing the need for advanced gunsmithing knowledge.
Using the jig, the builder drills the necessary pin holes for the trigger assembly and other internal parts. This is done with a hand drill or a small drill press. After drilling, the user must remove the remaining polymer material from the main cavity of the frame. This is accomplished with a rotary tool or a small router, following the guides molded into the receiver.
Once these milling and drilling operations are complete, the frame is considered a functional firearm receiver. The builder can install a lower parts kit, which contains the trigger, pins, and springs. The completed frame is then ready to be mated with standard components like a slide, barrel, and magazine, to create a fully operational pistol.
Legal Framework and Regulations
Historically, the legality of building firearms at home for personal use is based on the Gun Control Act of 1968. This federal law allows individuals who are not legally prohibited from owning firearms to manufacture a weapon for their own use without a federal license.
A regulatory shift occurred with ATF Final Rule 2021R-05F. This rule updated the federal definitions of “firearm” and “frame or receiver.” The new definition now includes weapon parts kits that can be readily converted to a functional firearm, directly encompassing the products sold by companies like Polymer80.
Kits that include an 80% receiver along with the necessary jigs or tools are now regulated as firearms. This means they must be stamped with a serial number by a licensed manufacturer. Sellers must be Federally Licensed Firearms Dealers (FFLs), and they are required to conduct a background check on the purchaser. State laws may impose even stricter controls, with some jurisdictions banning the sale or possession of such kits entirely.
The “Ghost Gun” Controversy
These firearms are at the center of a heated debate, often referred to as “ghost guns” by opponents and the media. This term highlights their defining feature: the lack of a serial number, which makes them untraceable by law enforcement if used in a crime. Gun control advocates argue this makes them a tool for criminals and others legally barred from purchasing firearms. They point to the increasing recovery of these unserialized weapons at crime scenes as evidence of a public safety threat.
Gun rights supporters and hobbyists view building a firearm as a protected tradition and a way to customize a weapon while ensuring personal privacy. They contend that criminals will always find illicit sources for weapons and that regulating kits penalizes law-abiding citizens. The argument is that focusing on the object itself, rather than the person using it, fails to address the root causes of violence.
This disagreement frames the ongoing political and legal battles over these kits. One side sees an unregulated pipeline of untraceable weapons flowing into communities, while the other sees an attack on a legal hobby and the rights of gun owners.