Jose;
Hopefully someone more knowledgable than me will come in with better info than I. As I understand it though the two rounds should have identical chamber dimensions except for the rim. There would be no danger created by the lack of the rim on the js rounds. The main point of concern here would be to ensure the chamber was cut to properly headspace the js as the jrs headspaces on the rim.
Another point & this one I am totally unsure of, but I seem to recall seeing at some point in time that the rimmed versions of these Mauser cartridges were often factory loaded to slightly lower pressures & balistics than were their rimless counterparts intended for use in the bolt actions.
The headspace issue is quite easily determined by use of a headspace gauge. Again hopefully someone with more knowledge of the pressure levels of the two will chime in. I do know that for many years the US loading of the 8x57 round was quite mild in defference to the many old 88 commission rifles kicking around, most of which did not have the S-Bore. Assuming correct headspace in the chambering this ammo would be lower pressure than even the jrs rounds so should be completely safe.
