My original question is mute because the shallow throat isn't the only problem with this barrel. After loading cartridges with the same bullets in the other cannelure, I found that the barrel will not fully chamber any 445 Supermag cartridges using Starline brass because the rim protrudes from the barrel not allowing the barrel to close on the frame. This occurs with empty Starline cases also. The barrel does accept 44 mag cartridges.
So the barrel has to go back.