kjohn, I once believed as you that all of the Norwegian rifles marked "7.62" were chambered for 30-06.
A few years back I picked one up so marked from a decent collector type in my area.
He told me that it was 7.62x51 but I was sceptical. I tried to chamber a 30-06 cartridge only to have it come up short. I then inspected the chamber with a bore light and it was obviously cut shorter with a sharper shoulder and less body taper.
Out came the headspace gauges and sure enough they fit the chamber perfectly, confirming the case type. Next, off to the range.
Still being a bit sceptical (my conservative streak) I tied the rifle to a lead sled and fired a round. The case extracted perfectly and there wasn't any distortion of the brass.
Feeling a lot better about the whole thing, I fired off another 20 rounds without a problem. The bore is almost pristine which is more than can be said of the stock. All numbers have been force matched and the stock has a rather crude repair, behind the bolt handle. It also is finished with that awful Norwegian spar varnish.
It's an OK only shooter. Shoots Hertenberger 7.62x51 into 2 in at 100yds and the South African stuff into about 3 inches.
I have'nt tried any handloads or commercial ammo in it nor will I. Other than a curiosity and maybe slightly rare, it's just a mauser. I love mausers by the way and Enfields and Springfields and Lee Enfields, Garands, I think you get the picture.
From your comment above, you to have a Norwegian mauser in 7.62x51. It's the first one I've heard of other than mine. How is it finished and does it shoot better than mine?