Studies performed in the Process Development Pile of the Savannah River Laboratory have provided precise measurements of the material bucklings of a number of D2O-moderated lattices of natural uranium metal rods over an extended range of fuel assembly sizes and lattice pitches. The 1-in. uranium rods were clad with 0.032 in. of aluminum. Fuel assembly sizes varied from single rods to clusters of 3, 7, and 19 rods (0.09 to 1.81 kg U/cm) and lattice spacings from 7.00 to 21.00 in., covering a range of moderator-to-fuel volume ratios from 10.23 to 161.53. A few lattices were studied at different D2O purities, in loadings of different sizes, and in reflected loadings.