Blow back pistols/rifles, like a .22 semi auto, or the 9MM AR15 pistols/carbines with no locking system on the bolt will sometimes spit a tiny ember of still burning powder out of the ejection port when the bolt moves to the rear. If you're standing off to the right side of the shooter, looking at the gun, you can see it. Sometimes you can see it, out of the corner of your eye, when you're shooting it.
Did I mention how dirty they get? My AR15 pistol and carbine will come home with a noticeable dull black "finish" on the upper and lower in the vicinity of the ejection port. If you touch that stuff your fingers come away blackened (powder residue that would go on out the muzzle if it had a locking system on the bolt like a .223 AR15) and they take some wiping/scrubbing to get them clean on the outside, let alone on the inside.
