[QUOTE=DesG;7877461]A few hundred degrees C? Soot? You’ve been watching too much star wars![/QUOTE]
Think about it, you have a quantity of black powder you have ignighted in a barrel behind a lump of lead, physics and chemistry now takes over, the powder is burning and expanding behind the ball this will transfer some heat into the ball so will the friction of the ball moving through the barrel, the fire ball behind the ball is easly a few thousand deg C, the only reason you dont get molten lead spewing out of the barrel is the thermal mass of the barrel and ball, they absorb some heat over the short anount of time they are in contact with the flames, this could heat the ball enough to give it the golden colour.
as for the soot, the combustion process in the barrel of any gun is not compleat (especially black powder) there will be some product of combustion on the back of the projectile, a very thin coating can change colour of the reflected light.