Remembering the RIFLE that was forensically proved to be fired from two separate hills held by Indians.
Recall that Custer and his 207 troopers were killed on the first day of the four days of fighting. . . and the natives looted all of those weapons in those soldiers possession on that first day. The battles from those others hills took place on the other three days as well as the first day, so it is reasonable to assume that the weapons from Custer's dead soldiers were pressed into service by the Indian Warriors who claimed them.
There is also an extant Henry Rifle where the forensics seem to match bullets and shell casings found both around the Custer battle and on those hills. It was likely brought to the battle by one of the Indian warriors since all of the shell casings associated with it seem to have been from Indian firing positions.
That makes three possible guns associated to the Custer disaster, with only one absolutely documented to have been there in the hands of one of the soldiers, the Colt.
The 1866 Winchester, being perhaps a soldier's personally owned carbine, is speculation based on letters and other ephemera. The Henry's presence is based on archaeology done at the various battle sites, finding cartridge casings and bullets that may match that Henry. The question is what are the possibilities that forensic comparisons with the extant gun and the markings, indentations, and rifling striations on approximately twenty expended shells and corroded lead bullets recovered 130 years after they were fired can be accurately compared with a bullet and casing fired from the same gun 130 years later after years of use and additional wear on the firing pin, chamber, and rifling?
Have you ever seen a bullet that's been a buried for even a few years? I think it may come down to a matter of wishful thinking opinion, especially with the heavily corroded bullets.