My experience with sights on 'cut-down' Krag rifles - FWIW:

A snug fitting 1903 or '03A3 'banded' front-sight will probably stay put with an application of JB Weld glue, (especially if there is a flat, dovetail, or spline-groove on the barrel). It can later be removed with a bit of heat and a plastic mallet.

The height of the front-sight blade and rear-sight notch, (above the top of the barrel), and the distance between the front and rear sights (if the barrel taper changes sight height), will all influence the angle of the bore, in relationship to the target.

Different bullet weights and profiles will likely have different trajectories. This is solved by 'sighting-in' for specific loads and recording rear-sight adjustment. This allows return to  'load specific settings' at future shooting sessions.

An original model 1898 Krag rifle (30" barrel), front-sight blade 'top', will be approximately .665" to .675" above the top of the barrel.

A 'cut-down' Krag rifle will often have a barrel that is 22 to 24 inches in length. If fitted with a 1903 Springfield 'banded' front-sight with a commercial blade, the height of the blade above the original barrel surface, (not the stepped part), often is about .665" to .674".

Although the front-sight heights in the two examples seem the same, they are different.
The 'cut-down' rifle's front sight is 8 inches closer to the rear-sight.
Due to barrel taper and the 1903 band being on a machined step, a higher front-sight blade has been used for the measurement to be similar.

This changes the angle of the bore (downward) and likely the 'cut-down' will shot low.
Moving the rear-sight slide to 200 to 300 yards will likely have the 'cut-down' shooting close to the 'point of aim' at 50 yards.

Attached photos:  A model 1896 'cut-down' with a 1903 front-sight (blade height .675" above original barrel surface). 50 yard targets from two different loads. Rear-sight settings from 200 to 300 yards were used

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