The ARC-920 Railgun was one of our earlier large-scale Halo weapon builds and another project where we learned a lot about turning game geometry into a physical, convention-ready prop.
The build began in 2018, although I didn't get around to documenting it on the 405th until the following year. This Build Log consolidates that original documentation and walks through the project from the raw game file to the finished Railgun.
Project at a Glance
Prop: ARC-920 Railgun from Halo 5: Guardians
Scale: 1:1
Source: Halo 5 game model
Construction: 3D printed multi-part assembly
Finishing: Sanding, filler primer, Bondo, and paint
Final Scheme: Black and tan with hand-painted details
Preparing the Railgun for Printing
Like many of our early Halo projects, the Railgun started with the original game geometry.
That model needed significant cleanup and smoothing before it could become a printable prop. Based on lessons we had learned building our Battle Rifles, I also wanted to divide the Railgun into as few pieces as practical while keeping it full scale.
Because of the size of the finished weapon, the joining and registration features also needed to be substantial enough to create a durable assembly.
All the parts sliced up and ready to go
Printing the Parts
The majority of the Railgun printed without too much trouble.
The most difficult area was where the two main rail sections joined, which required some adjustment to the support settings before I was happy with the result.
Eventually all of the parts were finished and laid out together, giving us the first real sense of just how large the completed prop was going to be.
Railgun fresh off the printer, toy for scale
Assembly and Surface Finishing
Once printing was complete, the Railgun was assembled and moved into finishing.
That meant the familiar cycle of sanding, filler primer, more sanding, more filler primer, and Bondo wherever additional filling was necessary.
Main Body post Bondo for seams
Parts after basic assembly and seam filling
Once the surface was where we wanted it, the main body received its first black paint.
Post black base coat
Masking and Paint
From there, the Railgun went through extensive masking before the tan sections were painted.
Pulling the masking away was one of those particularly satisfying moments in a prop build—the contrasting colors finally made the finished design start to emerge.
All masked up ready for tan paint
Post Tan paint, masking removed
The remaining smaller details were then finished by hand.
Hand Painting the details
The Finished ARC-920
With the detail painting complete, the Railgun was ready for its first convention outing—and, fortunately, it even fit inside one of our existing gun cases for transport.
The finished ARC-920 Railgun
Not long afterward, I paired it with the Recluse armor at a convention.
Railgun with our Recluse armor
I wish I had documented more of the modeling and preparation work at the time, but the photographs that survived still capture the major stages of the build.
Like many of our props, the Railgun may continue to receive upgrades over time, but I was extremely happy with how this version came together.
The finished Railgun
Looking Back
This build came from an earlier period in Alpha to Zeta's 3D printing work, and our modeling, printing, assembly, and finishing techniques have continued to evolve since then.
Even so, many of the fundamentals are still the same: prepare the model with the physical build in mind, minimize unnecessary seams, create strong alignment points, take your time during surface finishing, and let the paint bring everything together.
For more of our Halo builds, check out the rest of our Build Logs.
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