During manufacture the barrels of double rifles require "regulation" to ensure the bullet paths from both barrels are aimed at a common point of aim. This can be done to ensure either the bullets 1) parallel each other closely at all practical ranges, or 2) converge at a given range, beyond which they begin to diverge. Because of the need to regulate a rifle to a specific loading of its chambered cartridge, once regulated a double rifle cannot satisfactorily shoot bullets of different weights or velocities, as it usually affects the accuracy. The process of regulating a double rifle’s barrels is complex and can be time consuming, significantly adding to the cost of the rifle.