Decker 380 Build Kit

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 side loader or top loader, 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.

Decker 380 Build Kit FAQ

What’s in the Box