We need a bit more information.  Can you provide some pictures of the rifle, or a more complete description.  Look at some pictures of the M1894 rifle and 1912 carbine and see if it look more like one than the other.  What is the barrel length?  Has it been "sporterized"?

Yes, 6.5X55 is the correct ammo, BUT there is some genuine concern regarding the use of modern high-pressure ammo in these rifles.  You really should not use ammo designed for the Swedish Mauser, but lower-pressure (<40,000 psi) ammo designed or hand-loaded for the Krag.

139 grain bullet --
from wikipedia article:
    * 6.5x55 a 6.5 mm (0.256 in) rimless round. Most variations are loaded for a chamber pressure of 350 MPa (roughly 51000 lbf/in²). Early rounds, with a 10.1 grams (156 grains) long round nosed bullet (B-projectile) had a muzzle velocity of around 700 m/s (roughly 2300 ft/s), while later rounds with a 9 grams (139 grains) spitzer bullet (D-projectile) offered a muzzle velocity up to 870 m/s (2854 ft/s).[1]

Note that 51Klbf would be altogether too hot for the US Krag which has a larger base and has intended clearance between bolt handle base and receiver, those tend to crack lugs with high pressure loads. 

The machining on Norwegian version is different, bolt handle base is supposed to bear on receiver as well as bolt locking lug, to give effectively 2 locking lugs -- it is supposed to be able to withstand higher pressure than US Krag.