In regard to the concern about the gas escaping from the left chamber and the DR may not be off face. I see two things from the photos.
1) there is no imprint of the cartridge rim on the left face of the action and 2) the rim depth of the chamber seems too deep. If the left chamber was reamed improperly then you have a significant problem.
Thanks Stephen!
The photo certainly looks like a very deep cut for the rim. This may be but please know this is a 375 H&H belted magnum. I have set of Go-No Go gauges for belted magnum. I will give them a try to check the depth.
