Mike,
In 1807, Springfield designed a light weight shorter 33-3/4 inch long smoothbore longarm termed "Indian Carbine" by collectors. The barrel was pin fastened and the lock was proportionately smaller. They were manufactured beginning in 1808. Finding an original flint survivor is extremely rare. Reconverted specimens in very good condition can sell for over $5000. Some collectors and researchers call them Model 1807 Carbines. Springfield inventory reports list them as "Carbines".
Some may have been altered in 1830 for cadet use at West Point. There are specimens extant with the stock shortened at the muzzle and a bayonet stud mounted on the top of the barrel.
I did not cover these in my book as they are not considered Infantry Muskets.
Kent