Steyr M95 bore diameter.

[Eaglelord17]

They also believed the bullet would 'obliterate' into the bore, i.e. the base of the round would expand into the grooves creating a seal. Most bullets of that era were open based 'cupped' bullets which would expand to some extent (for example I have some 6.5 Carcano surplus bullets which clearly show this type of design). This mentality is largely a carry over from black powder rounds which were primarily lead bullets (i.e. expanding more than a jacketed bullet). Much like the belief that they needed long barrels for velocity (a very large factor for black powder rounds, not so much for smokeless powder rounds). Back then the understanding of smokeless powder and building firearms based around it was pretty limited indeed (think Gewehr 88 and issues like lack of proofing, rifles blowing up in service, etc.). It took a while for them to gain a clear understanding of how it worked, and many wrong theories had the spotlight for a bit due to the fact they hadn't been disproven (think about things like early semi-auto experimentation and the fears a hole drilled in the barrel would greatly effect gas-pressure and reliability, etc.).

Another side note in the Austrian case originally the 8x50r round was a black powder round, and the barrels would have been designed accordingly. I am pretty sure both the M1888 Mannlichers and M95 Mannlichers had the same bore dimensions and twist rate (but not thickness), so that is also a factor.

The knowledge base for early bolt actions specifically the Gewehr 88s, and Mannlicher firearms is very limited indeed. Many wrong things have been printed over the years, and due to how many refurb programs happened to these rifles over the years it is hard to find a 'pure' example. These rifles are kinda find your own truth, rather than trusting what is in the books.