The transport critical current densities, Jc, of superconducting (Bi, Pb)2Sr2Ca2Cu3Ox/Ag tapes were measured before and after employing a special radiation technique, which leaves the grain boundary properties largely unaffected. We identify two regions separated by a temperature dependent crossover field Hgb–p. In the low field region, Jc is limited by the transport currents across the grain boundaries, which remain unchanged after irradiation. Above Hgb–p, Jc is limited by flux pinning. In this field region, the artificial defects optimize flux pinning and enhance Jc.