This report describes the work concerning interior ballistic calculations for guns performed at FOI during 2014. Current available computer codes can model the internal ballistic in 0-2 dimensions. However, in order to accurately model the ignition and the variation in muzzle velocity, three dimensional modelling must be used. For this reason a 3D internal ballistic code is now in development. This report presents an overview of current available computer codes at FOI and describes the ongoing work to develop a 3D fluid dynamic computer model.