The entire story of the Colt Buntline Special has been disputed and refuted. Colt records show no "Buntline Specials" were ever made for Ned Buntline (Edwin C. Judson). Long barreled SAAs were made, but none went in a batch to any known characters.
Most accounts have Earp carrying a 5 1/2" barredl Colt.
Incidentally, family members insist the name is pronounced "ARP". I served in Korea with a distant descendant of Wyatt's. Never met him, just an article in "Stars and Stripes."