I liked the simplicity of the original design, but wanted more oomph from a longer pull and fatter bands. I grew the barrel length from about 116mm to 200, and redesigned the wheel so it has more side room, and a sleeve that the bands lie on that rotates with the wheel. The only downside is that now you will need to use support when printing the wheel. I made the cogs slightly thicker than original since they are not as wide. P.S. - Flip frame top 180 degrees so the flat side is on the bed!
I did the wheel and trigger at .25 resolution, 3 perimeters, 2 top and bottom layers and 100% infill. THE WHEEL NEEDS SUPPORT. Frame done at .3, 3 perimeters, 3 top and bottom layers and 50% line infill. The barrel is at .3 with 3 perimeters, 0 top and bottom layers and 50% triangle infill. Used mostly Gizmo Dorks Translucent Red PLA, which I am finding to be pretty good. I noticed posts on the source about having to tweak the fit on the frame pins. I printed one in PETG and it fit almost perfectly, but the PLA version did require some additional fitting. Used a 5/16th drill bit on the holes and hit the pins with a small sanding barrel on a dremel, followed by scraping with a pocket knife blade. The fit is good and it stays together with no adhesive, but I keep spare bands around the handle for added insurance, and so I have extra ammo.