It would be great if a KCA Member were to find one of these rare Model 1898 Krag Rifles.  Frank Mallory lists 10 Krags that had alternative Rifling for Test Purposes:

#276119 - Metford Rifling Test, November 1900, .04" filet(?)
#276205 - ditto, .02" filet
#276387 - ditto, .02" filet
#276398 - ditto, .02" filet
#277299 - ditto, .04" filet
#277309 - ditto, .04" filet

At a later date four Model 1898 Krag Rifles were fitted with 'Cole elliptical bore barrels'.  (I imagine they were something like "Lancaster Oval Bore Rifling"):
#s - 364050, 364427, 364451, and 364703.

It is interesting that Springfield Armory was experimenting with Metford Rifling in 1900.  Around 1895-96, the British discontinued Metford Rifling because of severe erosion problems with Cordite smokeless powder in the .303 Lee-Metford.

  They went to Enfield Rifling, similar to U.S. Rifling, except Enfield has almost equal width lands and grooves, whereas 'Springfield rifling' has lands that appear about 1/3 to 1/2 the width of grooves.

(Attached drawing shows Rifling used by Danes in their Krags, that's suggestive of Metford rifling).
  I wonder how many grooves Springfield used on their 'Metford' rifling?

Sometimes it just pays to hit the 'text books'.  I certainly have gotten my money's worth and great pleasure from the works of Franklin B. Mallory, Ludwig Olson, and William Brophy (and Richard Hosmer, too)!  I think I'll take a vacation and read their works cover to cover, instead of jumping around for specific information, as I'm inclined to do.
  Rifling information contained in Mallory's "The Krag Rifle Story", 2nd edition, confirms that the early Danish Krags had 'Rasmussen rifling' that was derived from Metford rifling.
  This was replaced around 1925 with a concentric rifling (which reminds me a lot of a Model 1867 (11.5mm) Danish Rolling-Block, I use to have).  The 'small bore' smokeless era probably prompted many earlier ideas to be retried.

  The 'Cole elliptical rifling' was influenced by the Lancaster Oval bore rifling.  Dr. W.F. Cole, of Waco, Texas, may have been the first to apply this old idea to small bore, high velocity, jacketed bullets.  Springfield tests in 1902 showed some minor improvement in accuracy to 500 yards in the Krags equipped with the Cole barrels.  Apparently, several 1902 Krags were fitted with Cole barrels for International Matches, held at Ottawa in that year.
  Bullet jacket stripping with the Krag, 2,200fps ammo, (This ammo was later abandoned, due to bolt lugs cracking), appears to have prompted, November, 1900, tests with gain twist and Metford rifling.  Apparently, tests showed no advantages to these other rifling types.  Mallory presented the Springfield version of 'Metford rifling as using four lands and grooves.

The following Krag s/n's are listed in the 1902 Ordnance report as having been tested using Cole rifling. Some of the same rifles were tested with the standard rifling therefore, the Cole barrels likely no longer exist. Nevertheless, here are the serial numbers that are listed:

326616
323821
236616
364703
364427
364050
364541

The following four rifles were used with standard barrels for comparison with the Cole barrels:
399390
400586
400888
400638

In addition, Cole rifling was tested in the Experimental Springfield (Model 1901 or 1902 - not sure which) at the same time.

The Cole rifling was initially thought to generate superior results at 1000+ yards. However, this was due the 1:7 and 1:8 twist as compared with the standards 1:10 twist in the Krag. When they tested Cole and standard rifling both at 1:8 twist, the accuracy results were essentially the same. The Cole seemed to offer no advantage. There is discussion of hope that the Cole would reduce or eliminate the occasional jacket stripping that occurred in the standard barrel but the report does not state whether it did or not.

If nothing else, the inclusion of these serial numbers in the 1902 report confirms that these Model 1898s were all Rifles and not Carbines!