What do those stand for? I was looking on some of the common sized ones, and the TW was about 18 - 17.5, 18.9, etc. The WC was closer to 48. Most of the places exchanging tanks here only put in 17-18 pounds which is much less than the tank would hold if the WC is the weight charged, or weight of charge.

I have a smaller tank marked TW 10.5 and WC 10.2. It weighs 14 pounds now part full.