Square Bridge rear,,Can't see the front ring well enough to make out if it;s a double square bridge.

Straddle floor plate.
Possibly a Magnum length Mauser action(?)
The real Magnum length action, not just a standard action with the mag box cut & lengthened and the feed ramp cut back to make room for the extra length of the cartridge.
The extractor and ejection port look extra long to me,,at least the pics make it so.