Through research I discovered that one of the reasons that my textures were becoming so warped was because I was using the standard Unwrap option inside Blender.

https://www.youtube.com/watch?v=yc0b5GcYl3U

After watching this video I had an idea of how to proceed on unwrapping my Pawn model. Unfortunately this included coming up with a way to separate the sphere from the the rest of the mesh as in my first try I combined the two. I ended up box selecting most of the sphere and separating by selection.

After using the sphere unwrap option and following the alterations in the video above I managed to get my sphere UV unwrap to look like this. As you can see however I didn’t manage to select the entire sphere, I wasnt too worried however, as this was mainly just a test to see if the texturing results would be better after using this way of unwrapping my mesh.

I used the cylinder unwrap option for the rest of my model.

Bringing these two unwraps into Substance Painter, I was much happier with the results I was getting.

The seam on the sphere is pretty obvious here, but there doesn’t seem to be any stretching happening. However there is quite obvious stretching happening on the part below the sphere. This means that I still haven’t worked out the right way to unwrap complex meshes like the one above and that there is more experimentation needed to get this right.

Jon suggested that the reason I was getting stretching was also because I hadn’t applies rotation and scale. I can do this by going into object mode and using ctrl-A to bring up the menu. Once I had done this I unwrapped the main body of the Pawn again by using smart UV unwrap. This time my UV looked like this:

I brought this new mesh into Substance Painter to see what the result was.

I havent got all the layers on it yet, but as you can see already the stretching that was happening before has pretty much been solved.