|[ن - م] Following [ ن ] and Tanwin|
Both [ م ] or [ ن ] become Mushaddad when they are preceded by a word ending with a Sakin [ ن ] or Tanwin.
[ م ] also becomes Mushaddad when preceded by a word ending with a Sakin [ م ]. This rule does not apply to initial [ ن ].
In these cases, the pronunciation of final Sakin [ ن ], [ م ] or Tanwin would be assimilated into the initial [ ن ] and [ م ] of the following word.
Notice that initial Mushaddad [ مّ ] and [ نّ ] are pronounced with Ghunnah.
Remember: The duration of Ghunnah is two counts [Harakah].