Found this file on sketchfab, converted it to stl, fixed it in 3D Builder and split it up so I could print it full size.

Supports needed

this is the information on the firearm itself:

The Thunder was first revealed at the 2004 SHOT show along with a few videos, produced by Triple Action, LLC of Logan, Utah. Triple Action looked for a production company to license the design to. The gun never entered mass production and Triple Action soon disappeared from the market entirely, leaving the whereabouts of the prototypes unknown.

The Thunder is a large-caliber single shot handgun loaded through a scissor breech in the back of the gun. A massive muzzle brake mounted on the barrel provides some recoil reduction, and a patented recoil reduction design (called a "Nitrogen recoil controller") was implemented into the gun to further reduce the massive recoil.

A small cocking lever is featured on the left side of the gun.

"Triple Action Thunder" (https://skfb.ly/6XnUL) by Ri-Ri is licensed under Creative Commons Attribution (http://creativecommons.org/licenses/by/4.0/).