WblDon, I highly doubt that your rifle was originally chambered for this caliber but more than likely for the .35Win or possibly a 9x57R like species.
I think that the conclusion I had from the proof marks posted on GB (IIRC) showed just that.
The .350 G&H is likely running at a considerable higher pressure than the .35Win.
Please make sure that the gun is safe before pulling the trigger.
Kindest regards,
WC-