FOI has developed and executed tests to investigate thermal Insensitive Munition (IM) modification of 12 cm SVINGGR M/58 Z. The present work follows a previous study called Termisk IM-anpassning av ammunition, (FOI-D--0833-SE). In the former study, different categories of IM modification were studied, and it was concluded to further investigate the modification of the depressurization on 12 cm SVINGGR M/58 Z. Slow cook-off (SCO) tests were performed with a modification of the depressurization of the fuze, i.e. the strength of the threads was modified. Modelling of the SCO test was also performed in order to support experimental design but also to evaluate the experimental results. The SCO tests show that it is possible to modify the response of a 12 cm SVINGGR M/58 Z by depressurization and thereby enhance the IM-properties and increase the safety. The technique should be applicable on other ammunition with melt casted charge.