If you are that interested to continue I suggest finding someone who is willing and capable of creating a CAD file for you. The worst thing to happen here is to find out how to not 3d print this part. I would think injection molded nylon will be far stronger than printed as layers go it solidifies then had to be "flash melted" for the next layer to adhere which could cause weakness in terms of repeated forces acted on the part.
I'll be back with a sketch to make a 3D model
F.Y.I.The smooth bore pistols can shoot BB's OR pellets.The rifled barreled pistols shoot only pellets.Hunter