How is it a muzzle loader has no brass case and they are safe and here we have a rifle stronger than a muzzle loader and discolored brass is going to cause dangerous over pressure?
The muzzle loader is basically sealed unit where the cartridge case "seals" an somewhat open chamber. The open section (somewhat unsupported for lack of a better description) is generally the web of the case which is hardened to support the chamber pressures. If softened enough by annealing then it could rupture. Your basic case failure.
Okay. Now answer the question
I did answer the question very clearly and succinctly. You simply choose not to understand.