In another post (which has been locked) there was a question about the authenticity of two handed shooting in the old west. This is a subject that I looked into a little bit a while back and found an interesting example.
On August 14, 1889 U.S. Deputy Marshal David Neagle was in a train station in Lathrop California with U.S. Supreme Court Justice Stephen Field. He had been assigned to protect Justice Field from a man named David Terry, who had threatened, and previously attacked the Justice with a bowie knife over a ruling in a case involving Terry's wife, Sarah.
Terry entered the railroad station where Justice Field and Deputy Marshal Neagle were sitting at a table and struck the Justice in the head. Deputy Marshal Neagle stood up and placed himself between Terry and the Justice, and ordered Terry to keep his distance. Terry, who was more than 6 feet tall yelled at the Marshal and reached into his coat, where he habitually carried his bowie knife. Fearing for his life and the life of Justice Field, the 5 foot tall, left handed Deputy Marshal drew his revolver from his hip pocket and using a two handed grip fired two rapid shots. The first struck Terry in the heart and the second in the ear, as he fell dead. After the shooting, it was determined that Terry was not in fact armed, and Neagle was arrested on a charge of murder by the Constable of Lathrop.
In addition to the lack of a weapon, there was a legal question over a U.S. Deputy Marshal's legal right to defend the Justice, as there was no federal law stating that such an act was authorized. The case (which became known as In re Naegle) was transfered to federal court and it was determined that Neagle was fulfilling his duty in protecting the life of Justice Field and the murder charges were dismissed.
This was an important case that strengthened the powers of the President by enhancing the authority of federal Marshals and their deputies. The court records preserved the details of the shooting, including Neagle's testimony which spells out his use of two hands to shoot Terry. This can be found in Records Group 21, U.S. District Court. Northern District of California, Circuit Court Civil Case 10469, Transcripts, "In the matter of Habeas Corpus of David Neagle" Regional Archives and Records Center, San Bruno, California.
While this dose not shed light on the popularity of a two handed shooting grip in the 19th century, it does show that it was not unheard of.