My method for these is pretty simple. I just sit down with a pair of calipers and a pencil and paper and make some sketches and take a bunch of measurements.
From there, I model the geometry in Alibre Design. The part that interfaces with the firing mechanism is going to be a bit touchy. So, I broke the model into two parts. This allows me to print the fist in an optimal orientation in the FDM printer and this critical part in its optimal orientation as well. This also makes iterating quicker, as I don’t have to print the whole fist each time.
After a couple of iterations, and a little bit of work with the file, I have a replacement fist that fits and fires similar to the original!
