They were called "horse pistols" because they usually were issued in pairs with a set of connected holsters designed to be draped over the pommel of a saddle. Horse pistols weighed several pounds each, and were so long they could not comfortably be carried at the hip. In fact, the belt holsters that we commonly associate with cowboys were not used in the era of Lewis and Clark.
In 1803 Lewis picked up a set of two horse pistols from the Schuylkill Arsenal in Philadelphia, where records indicate there were several hundred pairs on hand. The standardized U.S. military pistol of that period was the Model 1799 single-shot flintlock gun made under contract with North & Cheney of Berlin, Connecticut. This would most likely be the weapon Lewis chose because it could use the same .69 caliber ball as the standard U.S. military musket. It was 14Ω inches long overall, and weighed three pounds.
In addition to the North & Cheney pistols, Lewis could have chosen from over 100 horseman's pistols of an earlier model on hand in Philadelphia's Schuylkill Arsenal in 1803. In the late 1790s the U.S. Army ordered pistol barrels, locks and stocks from both European and domestic sources. They let contracts-for-assembly to various regional gunsmiths, supplied them with locks, stocks and barrels; the craftsmen returned finished pistols and charged only for their labor and incidental parts. The second pistol illustrated above represents these assembly-contract weapons. They were small caliber than the North & Chaney, so many historians conclude that Captain Lewis would have chosen the North & Cheney because of the convenience of interchangeability of bullets with the standard Army musket.
Early on the morning of July 27, 1806, while camped on the Two Medicine River in the upper Marias River basin with his three companions and eight young Piegan men they had met on the previous afternoon, Lewis was awakened by a shout from Drouillard: "damn you let go my gun!" The captain quickly learned that the Indians had seized all the men's weapons. He later recalled:
I reached to seize my gun but found her gone, I then drew a pistol from my holster and terning myself about saw the indian making off with my gun. I ran at him with my pistol and bid him lay down my gun which he was in the act of doing when the Fieldses returned and dew up their guns to shoot him which I forbid a he did not appear to be about to make any resistance or commit any offensive act, he droped the gun and walked slowly off.
Meanwhile, rest of the Indians were making off with the Americans' horses, a deed of even more threatening consequences than the theft of their guns. When Lewis called the horse-capturers' bluff, one of them took cover and called to the other. The latter turned to face Lewis, who shot him in the belly. The Indian returned fire, barely missing Lewis's head, then crawled behind a nearby rock. Lewis, having only one pistol in hand, and with his shot pouch still yards away, turned and "returned leasurely towards camp."
Since Lewis and his men had been on horseback, and he drew the pistol from a holster, it is almost certain that the weapon was one of the "horse pistols" he had obtained from the arsenal at Philadelphia.
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