You don't need a gunsmith to tell you that the cartridge for the Modelo Argentino 1891 or Modelo Argentino M 1909is the 7.65X53mm Mauser round. (BUT, it isa good idea to have a gunsmith check the HEADSPACE on any old military rifle before it is fired. Unless the previous owner has been shooting it with no problems!)
I'm not sure about the 1891s, but a lot of 1909s were reamed to chamber 30-06 to extend the service life of the rifle due to the endless suply of surplus 30-06 ammo from sugar daddy Uncle Sam.