When the client heads out with the PH, can the client bring two rifles, his primary and back-up?

I'm about to pick-up a scoped Dakota Model 10 in .375 H&H which is a very light rifle, hence easy to carry. If the gun bearer were to carry my heavy Jeffery, then based on the shot, I could shot either.

Or, shoot the Dakota then take the Jeffery big bore for any follow-up shot.

How much does a black-O-matic cost anyhow?