Found this in "The Prairie Traveler" by Marcy 1859
"This point is illustrated by an incident which fell under my own observation. In passing near the "Medicine-Bow Butte" during the spring of 1858, I most unexpectedly encountered and fired at a full-grown grizzly bear; but, as my horse had become somewhat blown by a previous gallop, his breathing so much disturbed my aim that I missed the animal at the short distance of about fifty yards, and he ran off. Fearful, if I stopped to reload my rifle, the bear would make his escape, I resolved to drive him back to the advanced guard of our escort, which I could see approaching in the distance; this I succeeded in doing, when several mounted men, armed with the navy revolvers, set off in pursuit. They approached within a few paces, and discharged ten or twelve shots, the most of which entered the animal, but he still kept on, and his progress did not seem materially impeded by the wounds. After these men had exhausted their charges, another man rode up armed with the army revolver, and fired two shots, which brought the stalwart beast to the ground. Upon skinning him and making an examination of the wounds, it was discovered that none of the balls from the small pistols had, after passing through his thick and tough hide, penetrated deeper than about an inch into the flesh, but that the two balls from the large pistol had gone into the vitals and killed him. This test was to my mind a decisive one as to the relative efficiency of the two arms for frontier service, and I resolved thenceforth to carry the larger size."
"This point is illustrated by an incident which fell under my own observation. In passing near the "Medicine-Bow Butte" during the spring of 1858, I most unexpectedly encountered and fired at a full-grown grizzly bear; but, as my horse had become somewhat blown by a previous gallop, his breathing so much disturbed my aim that I missed the animal at the short distance of about fifty yards, and he ran off. Fearful, if I stopped to reload my rifle, the bear would make his escape, I resolved to drive him back to the advanced guard of our escort, which I could see approaching in the distance; this I succeeded in doing, when several mounted men, armed with the navy revolvers, set off in pursuit. They approached within a few paces, and discharged ten or twelve shots, the most of which entered the animal, but he still kept on, and his progress did not seem materially impeded by the wounds. After these men had exhausted their charges, another man rode up armed with the army revolver, and fired two shots, which brought the stalwart beast to the ground. Upon skinning him and making an examination of the wounds, it was discovered that none of the balls from the small pistols had, after passing through his thick and tough hide, penetrated deeper than about an inch into the flesh, but that the two balls from the large pistol had gone into the vitals and killed him. This test was to my mind a decisive one as to the relative efficiency of the two arms for frontier service, and I resolved thenceforth to carry the larger size."
