One of my hobbies over the years has been as a student of Post Civil War settlement of the West, with an emphasis on Lawman and Peace Officers. For 3-1/2 years I was part of the Speaker's Bureau of the Arizona Historical Society. For years I read everything I could find on outlaws, gunfights and peace officers. The information and impressions I got paint a complex picture, as alluded to above. Many shooting resulted in many more rounds being fired than intended targets hit, and that was often at arms reach distances. The lawman and outlaws involved in these incidents probably didn't practice much if at all.
I've read a couple of reports of Wyatt Earp practicing. Hickok, who favored '51 Navy Colt percussion revolvers, was said to fire all twelve rounds from his two guns every day. clean them, then load them with fresh powder, ball & caps. Firing those 12 rounds was done deliberately and on more than one occasion he put on shooting demonstrations that wowed the bystanders.
My favorite character from that era is Jefferson Davis Milton. Jeff Milton was a lawman most of his life, starting with the Texas Rangers (he lied about his age) and ending as a Custom's Line Rider in the Arizona desert. While the Chief of Police for El Paso, Texas he faced down John Westly Harden. Despite reading everything I can find on him I've read nothing about him practicing, but he was known to be able to hit most anything he aimed at. That kind of skill generally needs some kind practice. Harden was reported to practice, dry firing in his rooms in El Paso so much the other residents complained.
Also, I had a gunsmith friend who in his youth was with the Border Patrol. He told me he grew up on a farm in California. His neighbor was Ira Aten, a noted Texas Ranger and Sheriff. My friend once asked Aten how he survived all his gun fights. He told his young neighbor that you just look down the barrel and go easy on the trigger. That sounds like someone who got a rudimentary sight picture and understood trigger control.
In all the reading and research I did there was little mention of actual practicing, but a number of them, like Milton and Aten above, were known early in their lives as "crack shots". That kind of skill and reputation had to come from someplace.
Dave