Update to this thread: I have just finished the mold for the arm guns. This proved to be a tricky mold to make. There is small detail and many undercuts.
My usual method of making a silicone mold would not work for me this time around. The last of the 5 gallon bucket of RTV had sat in the garage for a California summer, and was partially cured.
this meant a brush-up mold rather than pouring in one shot into a case. In addition to that, there was some doubt that my first layer of RTV would cure. I used the last of some old catalyst and I let it sit longer than usual before opening. The RTV is a little soft, but it cured.
I had to run to TAP plastics for some expanding foam but I think the result is something I am happy with.
weighing in at 308g, this is a 2lb foam-filled resin roto cast part. It picks up all the detail and there are no voids in the casting, so I can call this solid!