Do Mass Effect's Weapons Have a Specific Smell?

Is that for your Reyes fanfic?
I wish I could truly help you, but I'm not too familiar with the weapons situation. I think the codex (likely from ME1) mentions that weapons use metal blocks to fire projectiles in the thousands, so perhaps it could be a metallic smell?
At some point though, while Shepard was dead, they also switched to thermal clips to prevent overheating in the old weapons. Depending on what you want to use in your story... perhaps it's just either metal smell or a heated smell.
No idea about the material's smell, but maybe metal as well. Stay metal