I would leave it as is, that is part of it's history.

Is the rust part of history?

Reasonably sure now that this Krag was modified for the Cummings sub-target gun machine.  Note attachment points on barrel.  Unfortunately the hole are tapped and threaded so deep that I suspect it would be dangerous to fire today.  Two of the holes are directly beneath the chamber.

With respect to the rust, Give me a chance, I'm old and slow but I can be trained!  BTW the stock has cleaned up beautifully…practically mint!

Sorry guys, time got away from me.
SN is 399280
Cleaned up rather well, pity it's not shootable…or at least I wouldn't.

You could always re-barrel it for shooting, but I personally would leave it as is.  Much to valuable!  Great piece of history there...

1911Ron:

Short Answer - Virtual Target Shooting.

Longer Answer - The Sub-Target Gun Machine was a $600 device, that allowed training in Rifle Shooting skills and provided competition without ammunition or Range facilities.

The device worked something like a pantograph. A rifle was fixed to the apparatus. Through the use of counter-weights and pivots, the "shooter' supported the weight of the rifle and could move it freely. The "Shooter" aimed the unloaded rifle at a target placed a moderate distance away. The machine had been adjusted or calibrated so that a sharp "needle" moved in alignment with the axis of the rifle's bore. When the "Shooter" had the rifle's sights aimed and pulled the trigger, the needle would pierce a miniature target placed in a holder on the Gun Machine. The strike on the miniature target would give an accurate indication of the sight picture on the distant target at the moment of "Dry Firing". The results were accurate and repeatable, which allowed for competition and skill building.

The Sub-Target Rifle Machine saw use from about 1900 to 1918. In the U.S., The New York City - Public School Athletic League put 'Gun Machines' in all the High Schools and ran a huge competition program. The U.S. Military Academies had machines. In Great Britain and Canada, Military Schools and the Royal Navy (aboard ships) made use of the Machines.  The U.S. Machines used mechanical linkages and cables to power the 'needle'. The British machines (Wilkinson) used a battery powered solenoid.

The attached post-card is actually a "Sub-Target" with 'pin pricks' and a score of 20 (3,3,3,3,3,3,2,0,0,0,), "Fired" in the U.S.A. (An NRA Postal Match?).