Why auxiliary-cruiser guns did not equal cruiser gunnery

How did auxiliary cruisers achieve useful gun range without full warship fire-control systems?

They used improvised ranging arrangements that sometimes worked well, but their effective gunnery still did not match a purpose-built cruiser with central fire control.

The question distinguishes the range of the ship from the effective range of its guns. An auxiliary cruiser could obtain enormous cruising endurance simply by carrying large fuel reserves. Gunnery was harder: designers fitted several non-standard ranging systems, some more successful than others. The resulting performance could look remarkable for an armed merchant ship while remaining inferior to the coordinated fire-control installation of a conventional cruiser.