What does a fresh gunshot wound actually smell like at a scene, and does that change after a few hours?

You want to know what it smells like. Good. Most writers skip this entirely, and I've never understood that, because smell is the thing that hits you before your eyes even adjust to the light. Burnt powder, yeah, but that description doesn't do it justice — it's like someone touched a soldering iron to copper pipe and then lit a match inside an old radiator. The gunpowder smell is sulfurous, almost like struck matches, and it sits low in the room because it's heavier than air.

Then there's the blood smell, and it has its own distinct register. Fresh blood smells like iron and salt and something vaguely organic. It's a warm, wet, penny-in-your-mouth smell, and the volume matters enormously to how it hits you.

Now, what happens after a few hours is where it gets genuinely unpleasant to describe. The gunpowder dissipates fastest — within two or three hours in a ventilated space, that acrid burnt-match smell is mostly gone. This matters for your fiction because if your detective walks in and smells fresh powder, the clock is ticking short. Blood begins to decompose almost immediately at room temperature. Around the two-hour mark in a warm room, that fresh iron smell starts to go sour.

What I'd tell you to pay attention to for your fiction is that experienced investigators actually use smell diagnostically. If I walk in and the powder smell is gone but the blood hasn't turned yet, I'm thinking one to three hours. If I get both gunpowder and fresh blood together, I'm thinking very recent — sometimes I'm thinking the shooter might still be in the building.

Here's your hard-won advice: don't use smell as atmosphere. Use it as information. The smell tells your detective the timeline. The timeline tells them who had opportunity. That means the smell, handled right, is not color — it's plot.