Decker 380 Build Kit Overview

The Decker 380 is a fully DIY .380 ACP carbine that requires no traditional firearm components. Everything—the bolt, fire control group, and magazines—is either 3D printed or assembled from hardware store materials. If you’ve been looking for an entry point into semi-automatic DIY firearms that doesn’t require tracking down regulated parts or complex machining, the Decker is it.

This complete build kit includes the barrel, firing pin assembly, springs, bolt weights, and all hardware needed to finish your Decker. Print the files, open the kit, and build. No CNC work, no press fitting, no specialized tooling beyond a basic drill and hex keys.

What Makes the Decker 380 Different

Truly DIY Semi-Automatic
Unlike designs built around AR fire control groups or Glock components, the Decker uses a completely DIY bolt and fire control group. The bolt is assembled from printed parts, threaded rod, and bolt weights included in this kit. No hunting for in-spec FCG parts, no worrying about parts kit availability. Everything you need ships in one box.

Innovative Magazine Design
The Decker’s custom magazines integrate the feed ramp directly into the magazine body rather than the receiver. This design choice simplifies the printed receiver while improving feed reliability. Magazine springs are included in the kit—print the bodies and you’re ready to load.

Configuration Flexibility
The Decker can be built as either a sideloader or toploader, and both configurations are fully ambidextrous. Choose the layout that works for your preferences and use case. The file package includes everything needed for either configuration.

Accessible Build Complexity
The Decker was designed to be one of the easiest semi-automatic firearms to build. The metalwork is limited to drilling a few holes in bar stock—work that can be done with an inexpensive drill on a workbench. Compared to builds like the FGC-9 or Shuty, the Decker dramatically reduces the machining barrier to entry.

FRT Compatibility
The DIY fire control group can be configured for semi-automatic only or semi/FRT operation. The design accommodates both trigger configurations using the same printed components with minor assembly differences.

What’s in the Decker 380 Build Kit

Core Components
The kit includes a .380 Auto barrel, firing pin tube, firing pin, guide rod, recoil spring, trigger spring, safety detent spring, and two magazine springs. These are the functional components that make your Decker run.

Assembly Hardware
Two M5x380 threaded rods and one M5x240 threaded rod form the bolt assembly backbone. Two bolt weights provide the mass needed for reliable cycling. Twenty M5x25 socket head screws handle receiver assembly. A hex key is all you need for final assembly and field stripping.

Legal Compliance

The Decker 380 is designed for legal home manufacture under federal law. Key compliance considerations:

Rifled Barrel: This kit includes a rifled .380 Auto barrel. Using a rifled barrel is required for legal compliance—smoothbore barrels may classify the firearm differently under the NFA.

Overall Length: The Decker is designed as a carbine platform. Ensure your completed build meets minimum overall length requirements (16″ barrel and 26″ OAL for rifle classification, or comply with pistol/SBR regulations as applicable).

State Laws Vary: Some states prohibit home-manufactured firearms, restrict magazine capacity, or have other regulations that may affect the legality of building or possessing a Decker 380. Know your local laws before ordering.

Decker 380 Build Kit FAQ

Frequently Asked Questions

Where do I get the Decker 380 print files?

The Decker 380 files are available from DEFCAD. They were released in November 2024. We do not distribute print files directly.

What printer do I need to build the Decker 380?

Any standard FDM printer with sufficient build volume will work. The Decker was designed for accessibility and prints on consumer-grade machines. Check the file documentation for specific print orientation and settings recommendations.

What tools are required to build the Decker 380?

Basic tools only: an electric drill for hole work in the bolt assembly, hex keys for socket head screws (included use), and standard workshop items. No CNC, no lathe, no mill, no press fitting required.

Can I use a different barrel with the Decker 380?

Yes. The Decker supports multiple barrel options including barrel liners, ECM barrels, and Bersa .380 barrels. This kit includes a .380 Auto barrel, but the design accommodates alternatives if you prefer a different sourcing method.

What is the magazine capacity?

The Decker uses custom printed magazines with an integrated feed ramp. Standard capacity is approximately 20 rounds depending on configuration. Two magazine springs are included in this kit.

Is the Decker 380 legal to build?

Under federal law, individuals may manufacture firearms for personal use without a license. However, state and local laws vary significantly. Some jurisdictions prohibit home-built firearms or have specific restrictions on magazine capacity or firearm configurations. It is your responsibility to verify the laws in your area before ordering.

What is the magazine capacity?

The Decker uses custom printed magazines with an integrated feed ramp. Standard capacity is approximately 20 rounds depending on configuration. Two magazine springs are included in this kit.

Is the Decker 380 legal to build ?

Is the Decker 380 legal to build?

Can I sell a Decker 380 that I build?

Manufacturing firearms with the intent to sell requires a Federal Firearms License. Building for personal use is legal federally; building for sale is a licensed activity. This kit is intended for personal use only.