Your extractor needs to be replaced. The rim dia. is .534 which is almost identical to the belted .375 H&H and other standard belted magnums(.532).
Because of the longer length of the Mauser magnum action you need a longer extractor than the standard Mauser 98 extractor which would also work with slight modification for magnum rim. The CZ550 magnum
.375 H&H extractor will fit and you can pick one up from CZ USA for $35 bucks . They have it in stock.
Hope this helps.

https://shop.cz-usa.com/ProductDetail/526006705501_Extractor-375-550-Magnum