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.