im gonna ask an ignorant question. How can Mauser actions handle 8mm Mauser but can’t handle a .243?
Older Mauser actions, the 93 and 95 were not as strong as the 98. Most Chinese Mausers are copies of the 98 so should handle the 243 if it is a well made rifle. Sadly many were poorly made. I would have it checked by a gunsmith at the same time you get the chamber cast.