The 7x57mm was introduced in 1892 for the Spanish Mauser... They adopted it but did not get into production until 1893 so it is known as the '93 Mauser. Jack O'Connor loved to tell the story (columns in Outdoor Life). '93s were surplus (from Cuba among others) when he was young and the 7x57 makes a fine all around North American game round. BUT Point: Steel was not the quality/reliability then as now. Design called for pressure in the 45K CUP range. It was a very fine advancement for the time over black powder... Today with working pressure at 55K CUP right along... There was also a production of the Remington Rider Rolling Block rifles, military and civilian, in 7x57... Not the strongest action around. Fine for black powder...
You have a gun built for the more modern pressure and the brass has kept up strength wise. SO, many current loading manuals will give loads that are specified "modern guns only" to keep the fool from (ha, ha) using them in an antique Mauser rifle (or Remington). Pick up a manual or two and load to modern preformance for your modern rifle. You shouldn't be dissatisfied.
The other option is to find Norma ammunition. They don't have, apparently, the liability of USA and load to modern preformance levels. 7 Rem Mag it is not (or .270 WCF), but close enough that if you do your part... luck.
