This occurred to me, why waste time and Printing Material, printing 100% of a Prototype, when you can use ready-made stuff for the structural parts?
Leave the printing only for what's REALLY needed, like the moving parts.
I'll use here this Minimalist version of my ElastomatiK Rubber Band Gun, using 20 mm Diameter PVC tubing, but it's obvious any other Project can benefit from this shortcut...
Step 1: 100% 3D'd Vs Partialy 3D'd
Step 2: Boolean Cutting and Hollowing
Here's the start of the process, just hack away all the blurb, and hollow out some space for the tubes to fit.
Step 3: 3D Program's Cutting Tools
See the Cube, and the Cylinders? Just do a Boolean Operation, Subtraction, and subtract a cube, overlapping the space you want to hack, from the original Object.
Step 4: Final Tooling
Now, for the Barrel, unneeded parts cut, hollow out a space for the tube.
Step 5: How It's Going to Be
All other stuff subtracted, THIS needs to be printed.
So, you just 3D Print the Orange parts, and plug them around those 3 portions of PVC tube.
Align, glue, presto!
You've saved a lot of time, and Material, that way