Tom,
We seldom have dimensions that fit a known cartridge precisely. First of all we have to measure the chamber instead of a cartridge in most cases. The chamber has to be larger than the cartridge,right off the bat,otherwise it won't chamber.The question becomes,"how much larger and in which dimensions?".
There is no hard and fast answer to this,due to differences in the "designed allowances" and tolerances between the different manufacturers. Bullet diameters are a major source of misunderstanding also. Old cartridges very seldom fit the barrels in the manner we usually insist on. What this all means is we seldom find a cartridge, which has dimensions the same as we deduce from the chamber will be required.We then have to just use our best judgement or guess in finding the nominal caliber designation. Walmart is not going to have any ammo for these old rifles anyway, so it doesn't matter what you call it. What matters is being able to find or make cases and bullets to fit the rifle.Then,you can just call it what ever you think would fit best.We don't have this problem with more modern calibers,and the more modern rifles are usually marked in some manner.Based on dimensions given above(may change with chamber cast)I think the 8x50R Lebel case will fit the best and for bullets, either "as cast" 43 Spanish or sized 43 Mauser.The rims may have to be modified to "A"base or "MB" type,but this isn't much of a problem.Just something to consider.
Mike
