I don't know what the percentage is, but it is considerable, just go to any /k/ and you'see one or more anime threads.
Also many anime and manga have strong /k/ undertones, Ghost in the Shell, Gunslinger Girl, Girls und Panzer, Black Lagoon, etc.
I can relate, guns are cool and their mechanical aspect attracts a special kind of autism.
This phenomenon is so real that the opposite is also true, take for example the videogame Escape from Tarkov, nothing about it is otaku in any way and yet it attracts a lot of "otakus"(ahem like me) and even has plenty of anime artwork, the armed forces of most western nations are also full of weebs.
IMO there are similarities between operator autism and otaku autism, but I can't fully explain why and how, I just observed that there are.