From what I have read on this forum (but,I have to seach where),the maximum a German loc could carry was 400 ton of freight (10 wagons of 40 ton,the weight of an empty wagon also being 40 ton)
On" the most valuable asset of the Reich" P 9O (partly available on the net),I found the following:
-Germany operated daily 25000-30000 trains (which is corrobating my figures of the loc's)
-the car twinaround day (the time needed to goand return,loading/unloading included/or not ?) was the following:
september 1939:3.9 days
october 1940:4.4
late 1941: 6
We also know that most railway capacity was tied elsewhere,ans was not available for the east .
1)Let's assume that the German railway capacity in the east was 12 million of ton (= a minimum of 30000 trains,a lot of trains were carrying less than 400 ton)
2)What would be the available capacity if the war in the east was over in october 1941?
a)the occupation army and the civilians would claim 4 million ton (for some 1.4 million of men)
b)remaining 8 million of ton,but,to produce and transport to Germany one ton ,an other ton would be needed(the factories in the Urals would need oil,coal,raw materials,to be trasported by the railways,claiming ...coal)
c)remaining 4 million of tons :let's take 1 million of coal,one million of oil,one million of food,one million of ore (of anything)
d) to produce these 8 million (of which only 50 % would go to Germany),Germany would be obliged to export an enormous amount of machines,machine-tools,even coal to Russia,and the whole result would be a net loss for Germany .
Everything was depending on the railway capacity in the east,and,as this could not be increased,the whole thing was a non sequitur (the Russian railways could not be used,the whole system had to be transformed to German norms,in the OTL,the Germans occupied only a small part of European Russia,in the ATL,they would go to the Urals,etc.....,the local population had to be feed,which also would claim railway capacity )
Looking at
this page, the average wagon load fell somewhere between 11.7 and 12.1 tons from 1941 to 1944, a figure indirectly reinforced by the fact that the
average daily coal car placings were counted in 10 ton units.
This Wikipedia page tends to confirm the figure, with most payloads falling between 10 and 15 tons.
Regarding railroad capacity being "tied elsewhere", I already provided figures indicating that by the end of 1942, 20% of the German rolling stock was assigned to the Eastern Front.
Taking a figure of 10 tons per wagon and multiplying by 200,000 (the December 1942 Eastern wagon count), we get a total of 2 million tons of freight, which multiplied by a year (i.e., 365) gives the tremendous figure of 730 million tons in carrying capacity. Obviously not all 200,000 wagons were arriving / departing the Eastern areas every day, and dividing by the figure of 6 days of twin around time, we'd get slightly over 120 million tons.
Of course, the 6-day figure was the RB's average, and probably more or less approximates twin around time in the Zone of the Interior. You previously mentioned a figure of 8 days for the Eastern round trip. Let's say we adjust for loading / unloading and double the RB's 1941 average: this would give us about 60 million tons in carrying capacity
in a single direction, which is probably still too high considering that some of the wagons assigned to the East were passenger cars and that the distances involved might be somewhat off. Still, the yearly capacity must have been many tens of millions of tons, with my best estimate falling somewhere around 35 million tons (which fits nicely with
over 200 daily trains each at 400 tons), and not the 12 million tons you mentioned.
You then have to account for the
Germans producing over 60,000 new train wagons a year, which, if fully allocated to the exploitation of the East, would add about 10-15 million tons of freight capacity each year.
Considering that a significant part of all this rolling stock could serve both the needs of the field forces (on the departing trip) and of German industry (on the return trip), especially in HG Süd's sector, I think that Germany was quite capable to significantly exploit the East.