I keep coming back to the M1 Carbine as my GO TO HD Weapon

[M94/14]

I consider myself lucky enough to still have eyesight good enough to use the Carbine`s factory peeps sights, and prefer them over anything else. However, there are some optic mounts that replace the hand guard that look promising. It would be a way to update the Carbine`s usefulness to those that might have lost some visual acuity over the years, without permanently modifying the gun in any way.
I would however, not choose a rare collectable for this purpose.