Black Soot is normal on the tailpipes, it happens to all Vehicles, the "Black Stuff" in any combustion process is carbon as a result of an imbalanced chemical reaction leaving behind carbon with no oxygen to combine with to form CO2; ex: rich mixture.
Anything from cars to the pilot light on your natural gas water heater, to random crap you burn with a cigarette lighter.
A burst of black exhaust in a car is normal immediately following a transition to WOT. This is called "accelerator pump" logic or tip in enrichment, air flow changes in an engine are instant, while fuel metering lags behind because the computer and fuel system can only respond to what JUST happened, not predict whats GOING to happen, even just starting the engine will cause this effect. During this moment there is a brief opportunity for knocking and engine damage to occur if the fuel system doesn't respond fast enough to the sudden unpredictable increase in airflow, compounded by the fact that this usually occurs under the heaviest load condition at lower RPM since you are accelerating and starting a pull.
To compensate, when a sudden swing in the TPS and manifold pressure occur, an extra unmeasured shot of fuel is blindly added on top of the normal load/RPM value in anticipation of the incoming air to keep the mixture on the safe side during this chaotic transition. Too rich is better than too lean. This value cannot be measured or predicted by the computer, it is a static value. This enrichment shot only lasts a second or two until the transition to WOT completes and the sudden change stabilizes and becomes steady state.
On any kind of high performance engine with high compression like the Hemi engine, this can be very rich, especially with the factory settings where they have to account for the worst possible climates, temperatures, terrible fuel octane, owner abuse, etc.
Normally a catalyst will clean up much of this and burn the remaining fuel, but on a higher performance engine black smoke on hard acceleration is normal. It doesn't matter if it's gasoline, diesel, natural gas, anything involving HC + O2 combustion. So over time and little by little a coat of soot will form on the interior of the exhaust system, all the way out the rear Tips. Hope this helps.