A description is presented of an experiment which provides verification of the accuracy of the available neutron cross sections for use in transport calculations of deep penetration of neutrons through up to 3 ft of iron and 18 in. of stainless steel. Calculations of the experiment were performed with a special version of the MORSE multigroup Monte Carlo code which uses point total cross sections. Comparison of the calculations using the new MAT 4180-Mod 1 iron cross-section set with experiment indicates that the absolute neutron leakage spectra above thermal energies arising from scattering that penetrate up to 1 ft of iron or 18 in. of stainless steel can be calculated to within ∼20%, and that the total neutron leakage above thermal energies penetrating up to 3 ft of iron can also be calculated to about the same accuracy.