D. Scott Chatfield
To measure the Tichy tank's volume I took this thingie called a "scale ruler" and measured the model. Using the HO scale side, of course. Since a tank car is not a simple cylinder, a little estimation is in order. And since we need inside diameter, you have to subtract a bit from the measured outside diameter, but not much.
So I used an ID of 84" and a length of 32'6". Thus the math is:
42 x 42 x 3.1415 x 32.5 x 12 = volume in cubic inches, divided by 231 to get volume in gallons.
Please note the volume of the dome in general service tanks was supposed to 2% of the tank's volume, and that volume was to be the part of the dome above top dead center of the tank barrel. So the useable volume of the tank barrel (the volume stenciled on the tank end) should include that part of the dome below top dead center of the tank. I didn't feel like doing that math.....