Some pics of the construction.
Mostly it's self explanatory. All using hand tools except a jig saw to cut the outline. I use an Ipe plank and a template that I made after making a few adjustments to the shape. I trace it on the wood and cut it out. I use a mortise tenon joint with epoxy to secure it. You can use a pin instead. With the epoxy however it feels like it's all one piece.
The trigger guard is made from a piece of stainless steel from west marine. It costs $12 and I don't know what it's used for. It's the perfect length and has a hole at each end which I use for the screws. I enlarge the hole though for the head of the screw to be flush. Bending it into just the right shape can test your patience.
I'm right handed so I add a little contour to the right side with two part epoxy putty. You can do this with more wood. I then coat the whole thing with Herculiner to make it grippy. There are other methods that can be used to achieve this like epoxy and salt or something along those lines.
If you're doing this on a thin stock like a Riffe competitor reduce the thickness of just the tenon or you won't have enough wood on each side of the mortise to hold it.