The SPAD XIII has a rather poor arrangement of guns and gunsight so that you can only see part of the sight and the gunfire goes to the extreme left of the sight. The original model from Aviaskins was even worse because you could not see where the gunfire was going at all. I designed the present arrangement but I am well aware of its failings. Here is a picture. The guns are firing but unfortunately the picture doesn't pick up the tracer trail.

I have now changed things. The gunsight telescope had to go because it served no useful purpose and it blocked the view of the sight. Gunfire now goes to the centre of the sight as it should. I have also pulled the camera point back a little. It is not apparent from the picture but it gives you a much better all round view which is important with these biplanes and their intrusive top wings.

If you want to make this change you can download my fix here: see new link at reply 6 down the page.
This is arranged as a JSGME mod for DOF. Just put it in 'My mods' and activate like any other mod.