Accurate inelastic scattering measurements are of interest to improving modelling and simulation of advanced reactor systems through better nuclear data (OECD-NEA, High priority request list for nuclear data http://www.nea.fr/html/dbdata/hprl/). Two setups are available at IRMM for measurements of inelastic scattering with the (n, n′γ)-technique. The first the GAINS gammaarray for inelastic neutron scattering at a 200 m station consists of eight high purity germanium detectors, has high incident neutron energy resolution and is therefore tailored for inelastic scattering measurements. The second, at a 30 m station was developed by IPHC with the purpose of studying actinides for the Th/U cycle and emphasizing besides (n, n′γ) also (n, 2nγ) reactions. In the recent past a number of efforts were started to investigate the uncertainties and corrections required to obtain reliable results and to investigate the limits of accuracy of this technique. A joint effort is described that has led to an improved understanding of the fission chambers used. In particular, the important corrections to the efficiency for fission fragment loss were investigated.