This model was designed in FreeCAD - FOSS (Free and Open-Source Software) 3D parametric modeler. Source file is available.
Requires aluminum tube 8x890 mm (blue cylinder on the images). Use it as a guide and glue it in last.
Requires glue!
Update! 16 November 2024: Part “barrel_end_1_x1” was updated.
The author marked this model as their own original creation.