The proper way to make an Ackley Improved chamber is to disassemble the rifle, remove the barrel, and set up and chamber, and polish it on a lathe.
Some quick-and-dirty gunsmiths simply do the re-chambering with the barrel on the action. This frequently makes for misaligned chambers.
It's a simple machining operation, but done incorrectly, the new chamber will not fireform factory ammunition correctly and brass loss will be high.
John