I managed to assemble the complete milestag gun housing today and I've had to address a few issues whilst doing so.
Here is a picture of the completed gun housing
And another showing the mounted lens
As mentioned in my previous post, the recessed radii I use to mount exisiting circular objects (e.g. lens, barrel) were imperfect so I had to use a half round file for the barrel mounts and a Dremel with a bur for the lens mount.
Secondly, the RepRap'ed parts are not perfectly square and made worrying cracking noises as I tightened the self tapping screws. Upon disassembly I noticed that some of the plastic layers had detached from their immediate neighbours due to the stresses of straightening out the housing as the screws were tightened.
I've managed to repair the damage with ABS solvent and this seems to have generally strengthened the parts as the layers are all now fused together (on the outer surfaces at least).
I believe that the ultimate solution to this is to sand flat any imperfections on a linisher before assembly.
The next step is to paint the ABS with a solvent based paint and fit the electronics.