Sendero's rear-sight is a 'bitsa' put together, unofficially, from surplus parts. His sight is quite functional, but, did not come from Springfield Armory in its current form.
The base is from a 'model 1898 rifle sight' for the "hotter" 2,200 f.p.s. (220 grain projectile) ammo. This cartridge was 'short lived' and condemned, when U.S. Kragbolt-heads began developing cracks. (The Ordnance Department returned to the previous 2,000 f.p.s. (220 grain projectile) .30-40 cartridge.
The model 1898 sight bases had too low an elevation-ramp for the slower regulation cartridge, so they were scrapped and got into the surplus market. (The 'top' or Leaf part was saved and most were altered and used in a variation of the model 1902 sight).
The model 1902 sight-base has a higher elevation-ramp and uses a different shape of spring for the Leaf.
BTW - All 1898 and 1902 sight Leaves are graduated to "20" (or 2,000 yards) with the same spacing of increments.
The front and rear sights of Sendero's family Krag make it real likely it came from Stokes Kirk or Sedgley's Philadelphia shops.
Attachments: 1. model 1898 rifle sight. 2. model 1898 rifle base. 3. A 1902 sight with leaf officially altered from 1898 leaf.
Attachment 104478Attachment 104479Attachment 104480