We present the results of the gas gain uniformity tests performed as part of the quality control of the multiwire proportional chambers produced at CERN for the LHCb Muon system, along with a description of the last hardware and software upgrades. The test provides a relative gas gain measurement over the whole chamber sensitive area. It is based on the analysis of the spectrum obtained when the chamber is exposed to a 241Am radioactive source. Since the measurement is normalized to the peak of a precise pulse generator, the gain uniformity can also be evaluated among different gas gaps and different chambers
