I have a hunch on how this was done and it is not by a U.S. Arsenal or Armory.

Maybe a gunsmith did the modification for a VFW Post, but, that is just speculation.

My guess is that someone with machinery and skill cut the barrel to 24 inches. The stock was cut to the correct length to accept a bayonet and inletted to take the front barrel-band.

A 'step' was lathe turned at the new muzzle of the shortened barrel.

The barrel section with front-sight, that was 'cut-off', was bored out and cut to length to be a 'sleeve'.

This 'sight-sleeve' was positioned on the 'stepped-muzzle' and silver soldered in place. The barrel and sleeve were re-crowned together.

The shortened barrel-assembly was turned in a lathe to change and blend the contour from the rear of the 'sight-sleeve' to the front or rear of the front barrel-band. (The front band may have been stretched to fit a larger barrel diameter).

The bare metal from contouring was re-blued.

Recently I read an article in an older publication that indicated some Krag rifles were used for a federal program known as the bank robbery defense program. Basically after WWI surplus weapons were distributed by the fed and FBI to discourage robbery attempts by having the weapons distributed to the banks themselves as well as surrounding business to dissuade robbers from making attempts. The article indicated that the weapons would not be centralized to one location but to others others in the nearby area to create the idea of greater intimidation.
I wonder if this could be a source for some of the Krag rifles that were cut done in a skillful manner to reduce the overall length for easier indoors handling/storage but still also retain all the original parts such as the front bands to not compromise the original design characteristics.
The author suggested the fed in Indiana was known to participate in the program supplying Krags and SW m1917 revolvers to mostly rural banks, south of Chicago.
Noted examples were bank of Pierre Indiana, three Krags and three 45 cal revolvers, north Judson three Krags and two revolvers, Bank of Brook three rifles and five revolvers Waveland, Winimac one revolver for each teller and no rifles, other arms were distributed to nearby business's postal agents etc and so on.
Just a thought for a possible explanation for so many rifles that were skillfully cut down maybe by outsourced smiths to support the program.
I have not been able to find any more information regarding the matter at this time but found the information very interesting and a potential possibility regarding cut down rifles. Maybe someone is more informed on the subject or has heard of this before.