For those interested.
Lewis and Clark Official website regarding guns used
March 14, 1803 Letter to HF by Sec of War to provide guns
(4 months)
July 08, 1803 Expedition guns completed
(3 months)
October of 1803 Mod 1803 official full production starts at HF
(7 months)
May 14, 1804 After wintering in Camp Dubois, IL, Expedition actually leaves civilization to go up the Missouri.
Link to Expedition starting point details
"While Lewis went ahead on horseback to St. Louis, Clark and the crew got the keelboat up the Mississippi, and set up winter quarters on the Wood River in Illinois, opposite the mouth of the Missouri. Meanwhile, Lewis made friends, collected supplies, and gathered more information in the city. At last, on May 14, 1804, forty-two soldiers and hired hands embarked from Camp Dubois and proceeded up the Missouri toward the Pacific Ocean."
Obviously, there was no way that L&C had input to development of the 1803 and would not have used pre-production models of that rifle. They would have preferred to take well used Model 1792 Contract Rifles into the wilderness for several years. These guns were not made at HF but by numerous different contractors. It's doubtful that there was much chance of parts interchanability. Yeah, that makes sense.