Hmm, I'm sure I could find the real cause of this, it looks like a combination of tracer and muzzle effect, I bet I could get it to run with a little effort. Might as well make a version 6 of my mod? har har
I copied the line out this weapons file into your weapons file and it works just fine.
Luckily it was the second line in the file and made it easy to fine and replace.