A contributor to the Gunboards Forums, 'Ben74', tipped me off to the likely early 'ancestor' of the U.S. model 1892 Krag rear-sight.

The rear-sight of the Swedish model 1867-1889 rolling-block bears a striking similarity to some of the sights that appeared on Krag-Jorgensen prototypes and Test Rifles that came to the U.S.

The Swedish model 1867-1889 rifle was an 8mm update of the 1867 rolling-block. The rear-sight had an off-set 'notch' for volley fire. The volley 'blade' was incorporated into the rear barrel-band.

Some Krag-Jorgensen prototypes had a near identical rear-sight, but, the front volley sight was a blade on the right side of the front barrel-band.

It is easy to see the basic structure of the model 1892 U.S. sight in the 1889 Swedish rear-sight. The U.S. dispensed with the 'volley feature' and extra notch, but, retained the unusually long Slide.