I recently bought a customized and rebarrelled Norwegian(no groans please).  The action has matching numbers but was D & T for a side mount.  The stock is original but someone with some superior woodworking skills inletted a rolled comb and pistol grip into it.  The new barrel is shorter that the original giving the rifle a Mannlicher look. The gentleman I bought it from said that he thought it was re-barrelled in .257 Roberts, but there was no marking on it and he had never shot it.  I have done a chamber cast, and it is in .257 Roberts.  I have heard conflicting reports on the strength of this action and would like to shoot it.  Will it handle the .257 with the new barrel?
TIA

As long as you stay away from the +P loadings for the .257 Roberts you should be just fine.  I looked up the pressures at this link   (You need to Login; The only other concerns I would have is overall cartridge length and rim thickness for the extractor (the 6.5x55 Mauser round had a much thicker "rim" than the 7.92x57 it was developed from). The thinner rim of the .257 Roberts could have problems with the extractor being able to hold it properly.