Is this Val?

In discussing US Military 22 caliber Krags, differentiate between ordinary rifles fitted with Stevens-Pope barrels (high demand collectors items if in excellent condition) and the less desirable Gallery Practice Rifle (GPR).

GPRs come with two types of barrels.  Early production (?) has .226" groove diameter, 18" twist and were chambered for the .22 Extra Long rimfire.  Why that was done only the military mind can explain.  They function with ordinary .22 Long Rifle cartridges but are not very accurate.  They are surprisingly accurate with CCI Stingers and similar hyper-velocity rimfires, but that defeats their purpose.

Later GPRs are reported to have been made to conventional .22 Long Rifle groove and chamber dimensions.  I have not seen one of those.

The challenge with a replacement barrel would be fitting an extractor.  The extractor on the Krag bolt grabbed an auxiliary extractor.  The aux. extractor is what pulled the cartridge case out of the chamber and deposited it inside the Krag action.

Has anyone ever looked at the Lee Enfield .22 cal tube insert device? Could that be made to fit a Krag with the rimmed 30-40 chamber, similar to the .303 rim.

Just spit ball'in.

And Yes, I have several .22 training rifles. US and Foreign models.

The British Device was called a 'Morris Tube'. I have seen them in pictures on SMLE rifles and Webley revolvers.

IIRC - The Webley cylinder was replaced with a chambered block and became a single-shot.

The one for Lee-Enfield rifles likely angled down the bore and was 'off-set' at the chamber to take advantage of the issue center-fire pin and .303 extractor.