The rifling you describe is typical for 9.3x72R barrels and others designed originally for black powder, lead bullet cartridges. In Germany it is usually called "Expresszüge" = express rifling. It is the German version of the British "Henry rifling". Land diameters of 8.8 or even 8.7 mm are common. As the German proofhouses usually stamped the land diameter besides the proofmarks, we aare often asked "What's a 8.8x72 cartridge?" The smokeless 9.3x72R loads are essentially "nitro for black" loads. For these cartridges and lead bullet rifling the gunmaker Collath in Frankfurt on Oder river in 1905 designed copper jacket bullets with a short bearing surface. These Collath designed bullets are still loaded in current RWS and Sellier & Bellot 9.3x72R loads. A common substitute here is using soft, conventional .358" 200gr .35 Remington bullets, no Noslers, but Sierra, Hornady or Speer. Though undersized they will shoot quite ok, as the metal displaced by the lands will often fill out the grooves to a degree. A better bet is, of course, to find the correct RWS or S&B bullets or to use gas checked lead bullets.