So I have some design suggestions based on my own scans that I have made with Drac's Xbow and a NextEngine 3D Laser Scanner.
So this first thing might just be me, or my unwillingness to spend a few hours filing the print- BUT- there is a good amount of overhang where the grip meets the stock, The design is really clever, but I think a millimeter or two need to be shaved off the thickness of the arc.
You can see in my render that the middle finger ridge in the handle is pretty flat. It's just another flat landing area for your finger from what I've noticed.
If you ask me, the recession for this ridge goes in too deep. If it was flatter it wouldn't be a point that digs into your finger. You can see what I'm talking about in the image below:
Lastly, the extrusion coming off the base of the handle, is a little sharp. The real Xbow has more of a fillet, and the surfaces also blend together.
This is what I mean by that:
If you want to see some of the scan data I'm basing myself off of, you can find it here-
EDIT: Oh, and for those of you who don't check Nerf Modders Welcome- here's a photo of the finished print!
Ninja Edit #2: People have been asking me to provide the STL files, so here you go: