American English Phonetics

12.6.4 Syllabic /m/ and /ŋ/

In words like prism, bosom, rhythm, syllabic /m/ alternates with /əm/. Syllabic /m/ and /ŋ/ may also arise as a result of assimilation to a following consonant, as in I can go /ˈaɪkŋ ˈgoʊ/. Pronunciations like ribbon /ˈrɪbm̩/, seven /ˈsɛbm/, reckon /ˈrɛkŋ/ are less likely.