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.