While Walter Jenifer's attempt to merge several saddle designs into one proved inauspicious, the effort to do the same by Captain George McClellan proved quite successful. The experiments on the Hope, Grimsley, Campbell, and Jones saddles were well under way when McClellan submitted his recommendations for a cavalry saddle in early 1857. He had been sent on a tour of Europe to observe the tactics and equipment used by the European armies, but upon his return, he was more impressed with the American saddle designs under consideration. McClellan's saddle was a merger of the other experimental saddles, incorporating the cantle and sidebars of the Hope and blending the characteristics of the Campbell and Grimsley Dragoon pommels. The rigging bore traits of the Grimsley Dragoon and the Hope. One modification was made after the test, which was the addition of a rawhide cover that had made the Spanish and Hope saddles so durable.

McClellan retired from the military in 1857 to become vice-president of the Illinois Central Railroad, a position that was believed to be influential, from a financial and political standpoint, in assisting his saddle's acceptance by the review board. The McClellan was adopted in 1859 as the official saddle for U.S. troops, but whether or not his influence determined the decision, the saddle proved to be exceptional. Its simplicity, durability and light weight made it ideal for cavalry use. The large open slot in the tree and its deep gullet allowed the saddle to settle on a horse's back without abusing it- even when the animal lost considerable weight. The Confederates considered it quite a prize when captured.

By the second year of the war, Confederate saddlers were manufacturing copies of the McClellan with russet leather or even tarred linen rigging with varying degrees of quality. Although these were usually better than other Confederate "issue" saddles at the time, the U.S. models were almost always superior and it was a proud Confederate trooper who could boast of having a full set of Yankee tack and equipment. With slight modifications, the McClellan saddle saw service well into the 20th century, making it one of the longest issued pieces of equipment in American military history.