The below information from Rifles of the American Indians by Ryan Gale.
The Office of Indian Affairs
1849
Edward K. Tryon 1 rifle, 716 northwest guns.
I have to request that you will cause the following inscription to be placed on the rifle intended for the Chippewa chief:
Presented by Zachary Taylor
President of the United States
TO
Flat Mouth, principle chief of the Pillager Band of Chippewa
1849
Also, Chief Flat Mouth is one of 4 Indians who has their sculpture in the U.S. Capitol Building in Washington D.C. It is likely the Henry gun order document relates to the land treaties being signed in the various moves that occurred making new reservations. Many were created early 1850's with moves occurring 1855.
Ray