Updated parts 9-27-18: Added new pump handle files that I shaved material off of and added a feed adapter with an extruded collar for better fit to marker and improved angle of tube to rear support part. The feed neck may slice and print with a "plug" inside but my part was such that it popped right out and cleaned up easily. Some sanding is to be expected for best fit. All parts have been printed in PLA and have held up in games with little to no issue.
I also added a 10rd tube shaped solid part file that I used to print some spare tubes in vase mode at an increased scale of about 9.1 for diameter and however tall your printer allows. Used them all day and all 3 survived.
Inspired by the game Borderlands. Not an excuse, just an explanation. ;-) This is an old WIP sketchup project but the parts survived many games and the actual IM plastic of the marker broke from aggressive play rather than any of my printed parts. Ditched the BodyKit portion after one game due as it shifted too much from recoil. Files posted by request. FIF. Sizes should be fine but no guarantee. Pump handle parts have a design of sorts for a contrasting color but could just be lopped off in netfabb for a cleaner look. I've provided the sketchup files and the parts could be cleaned up a bit for better print results. https://youtu.be/82XqBc_Hqws
Some of the holes may need to be reamed due to the way the files turned out.