Booker makes a note to check Adachi's mental and physical health more thoroughly when they're out of danger, but what matters right now is the "out of danger" part.

As soon as Adachi has loaded his gun, Booker's shield drops and he ducks to the ground to rifle through pockets and scour the ground for the best weapons. He comes up with two nice-looking modern pistols, and a fair amount of pilfered ammo. As soon as Adachi returns to his side he pulls the shield over them again, and holds up one of the pistols, "Trade for the Mauser."

This isn't going to be fun for Booker. He likes his old guns. But what matters is getting the job done, whether he likes it or not.