I decided to do a quick 3d test of this method and see what happens. I didn't actually use any measurements, this is a complete approximation and not at all accurate, but it does show how this can work! Hope this is appropriate to post here.
A simple cone:
Fillet the long edge (cone should be more tapered, oh well):
Slice the hone horizontally, off-center (this measurement can be gleaned from the thickest part of the real grip):
Chop off the top:
Lay out the scribed lines. These are way off, sloppy (looks like an eBay replacement grip ha!). The line on the right is the original center of the cone. You need this.:
What I did was draw triangles (profile of the cuts you want) between the lines, then revolve them around the original cone center. This is like a lathe, it rotates the profile around a center line. I'm not sure what the SW equivalent would be, but I'm sure there's a function. Here's a closeup of the layout above:
Cutting the revolved triangles into the cone, you get this. Other than being mal-proportioned, I think it works! The rest is hand work, or fillets and stuff if working in 3d.
I hope this is helpful, or at least interesting.
Keep up the great work, you're almost there! I expect to see a BUNCH of blasters built on this.