Abstract: A countermass assembly is axially and radially restrained while within a vessel and is dispersible into its component parts upon being ejected from the vessel into an open environment. A plurality of groups arranged axially adjacent one another to form a stack. Each group is formed from a plurality of rings arranged in a nested interengagement. Each ring is an individual ring that is in a non-binding relationship with adjacent rings. The non-binding relationship allows each ring to be separable as such from its associated group when the stack is ejected from the vessel into the open environment.