Need help with german grammar. When can you have 5 consecutive german verbs?

To do this you would need to use pive voice with an auxillary. Ordinarily this would give you 4 verbs. but what about with a verb like fallen len, or schneiden len. as in the following fragment: "weil seinen Pistole h�tte fallen len m�ssen werden. " (or worden???) Is this sentence in correct grammatical form. (I'm trying to say: 'Because his gun had to have been dropped.') Is it possible to have 6 or more consecutive german verbs in a grammatically correct german sentence?