custom 375 ruger issues

[oldgutpile]

This one is for all the gunsmiths here on the forum:
Has anyone dealt with feeding issues in the 375 ruger? I recently bought a custom job on an Oberndorf mauser action. The original build (barrelling and metal work) was done by the late Bevan King out of B.C. The gun came to me second hand with a M-77 follower for the standard magnum cartridges (.532)
The magazine will only hold 3 rounds, but it either jams the second round, or blows it right out of the magazine, every time I eject the first round. Not a favorable scenario for a dangerous game cartridge! If I only load two rounds, it will pick up both rounds and eject them fine, but I am then limited to a "double rifle".
Some information I was able to find on the web, stated that the magazine box is undersized for this cartridge on most designs, and that these feeding issues are fairly common ( again, this is on mauser conversions, not factory rifles).
Has anyone on the forum here had any experience with this, and hopefully a cure?