Did a quick search... found the shootout story from 14 June 1882 in Llano, TX. It's detailed in a book called "The Mason County 'Hoo Doo' War, 1874-1902" by David D. Johnson. Story starts on page 228. Even has some background on John & Andrew.

Part of the book is online. Go to books.google.com and put "coggins llano 1882" into the search box. It should be the first result that comes up.

Don