When it comes to defining magnum cartridges, it’s not as straightforward as you might think.
There was a time when the term “magnum” was fairly well defined. I’m talking back in the 1960s and 70s when the word pretty much meant a cartridge more powerful than “normal” and was usually based on the belted Holland & Holland case. In fact, in the eyes of many, if it didn’t have a belt, it couldn’t be a magnum—that’s how synonymous the two words became. As always, though, there were many exceptions to the rule. Back in its early days as a wildcat, for example, the .25-06 certainly provided magnum performance if the standard for the caliber was the .257 Roberts. Yet it was never called a magnum.
At the other end of the .25-caliber spectrum was the .256 Win. Mag., a bastard of a cartridge if ever there was one. Originally designed as a pistol cartridge, what limited popularity it achieved was in the Marlin Model 62 Levermatic rifle.
Based on the .357 Mag. pistol case necked down to .25 caliber, as a rifle cartridge it was pitiful, sending a 60-grain bullet of low sectional density and ballistic coefficient at 2,760 fps. If we again cite the .257 Roberts as representing the performance standard for the caliber, it would have qualified as a super magnum compared to the .256. Incidentally, I actually owned one of those Marlin Levermatics, and the .256 Win. Mag. was the cartridge with which I started my handloading career.
Anyway, another and even better example of confusing nomenclature is the .220 Swift. When it was introduced in 1932, it absolutely blew the doors off any other .22 centerfire cartridge, yet like the .25-06, it never received the magnum imprimatur. Even when the .222 Rem. Mag. was introduced in 1958, the Swift pushed the same weight bullets about 500 fps faster, yet it was…well, just a Swift, not a magnum.