Good comment about the front stuffers burning powder 30 yards downrange. This effect is even more dramatic at night.
When you have a "magnum" muzzleloader and every time you fire it it is like Chinese New Years on Wahai Road, Shanghai, there is definitely a problem with the gun being able to handle said powder load.
To me, "magnum" is nothing more than a marketing term, much less a technical term. I have seen flashlights being called magnums, pistol and rifle cartridges being called magnums, even a Dodge automobile being called a magnum. On Cabelas, they have many nautical outboard motors referred to as "magnum".
What is the similarity here? There is one, the one being the bigger, badder, and meaner machine. That is a trend with all folks. Don't everybody love the thing that is the biggest, baddest, and meanest? Yes we do.
Now look at Buffalo Bore Ammunition. Their .44 Magnum cartridge produces app. 866 ft. lbs. of muzzle energy. Their .45 LC produces app. 1000 ft. lb. of muzzle energy! Of course, their .45 LC loads are super charged and meant for use in only certain firearms, such as Rugers, but still, see the difference here? What is magnum might not seem so when compared to more conventional namings.
What is "magnum" or not, is only in the eye of the beholder. Nobody can say who is right and who is wrong when dealing with this particular terminology. It is everybody's own opinion regarding what is "magnum" or not.