2-8-2 says I've been thinking on this all day...and I just don't get it.
From what I've read here, and elsewhere, on the "loads in/empties out" process, you're basically pretending to move freight. What I read from another source said that to pull this off correctly, I would need two sets of matching cars (including road numbers).
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Sadly there is A LOT of misinformation on empties in/loads out..The biggest is believing one needs a match set and that is one lie that should have never made print.Why? Does the prototype have match sets? The answer is a resounding NO! Then why do we? Simply put we don't.Again misinformation place forth by so called operation experts and operation expert wanna bes.

Why do I boldly state this? After 9 1/2 years working as a brakeman and years of railfaning I am yet to see match sets of cars or ANY freight car with the same number as another.It would be folly to do so because of car tracking and of course switching.
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What's wrong with pulling empties into the tipple, filling them by dropping coal loads into the hoppers, then taking them to their destination and pulling the loads out? They could then return to the tipple as empties again. This should work for on-line customers such as a power plant, coal dealer, etc.
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You could and it has been done by using coffee cans of scale coal and a open chute in the tipple.The cars are usually unloaded by a rotary dumper like Walthers makes or made..Now you enter the world of live loads. and should you have a derailment guess where that live load goes if the car(s) turn over?.
I never heard of it being done in N Scale though.
How would off-line traffic be simulated? I would still fill the cars at the tipple, but they would end up where?
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The BEST way is by using a stagging yard..Say you are modeling the Wheeling Division..The stagging yard would represent E&S other divisions and connections.This is how trains would enter and leave the Wheeling Division.