The /ŋ/ sound is spelled with <ng>. The /r/ sound is spelled with <rr>.
This is a contrast between a velar nasal continuant and an alveolar retroflex continuant, both voiced. Since /ŋ/ only occurs finally and /r/ initially, the only possible contrasts are medial and there are very few of them.
The mean density value is insignificant at well under 0.1%. The lists make 3 semantic distinctions, a loading of 75%.
banger Barra singer sirrah singers sirrahs tangy tarry
John Higgins, Shaftesbury, December 2010.