Originally Posted by
Dick Hosmer
The M1866 sights are a puzzle. They can occur with the sight reliefs facing either way. Of course the base (which utilizes a dovetail and one spanner-head screw) only goes one way on the barrel. It must follow the barrel dovetail. This also affects the pivot screw being towards the muzzle or the breech. Muskets, and the M1865 (1st Allin) have the pivot screw, and dovetail, to the rear. The M865 has one hole in the leaf and one notch at the top.
The M1866 with its' two holes in the leaf (and the subsequent models of 1868 and 1870 which have a similar base but entirely different long-range leaf) have the screw and dovetail in the front. The "correct" orientation of the relief cuts would be toward the muzzle, so as to present the sharpest picture to the shooter's eye. Therefore, the reliefs should be visible when the leaf is down, but not all are.
The "1867" cadet is a term of collector convenience, since they have special (thin) lockplates bearing that date only, whereas all other early TDs use the normal musket plate, dated 1862-1865. It is a completely miniaturized (even the band-springs are shorter!) version of the M1866 rifle, whereas the M1869 cadet is simply a shortened (but not extensively reworked) version of the M1868 service rifle. The 1867 has the sight pivot to the front, and, like the M1865, has but one hole in the leaf.
Hope that helps.