Magnums were created to make money … to sell more rifles and ammo. Thus, we have 3-inch, 20 gauge magnum shotshells that launch payloads with less velocity than standard loads. We have a .17 Hornet that throws a 20-grain bullet 3,600 fps, and a .17 Win. Super Mag. that throws the same 20-grain bullet 3,000 fps.
In 1963, Weatherby released its .224 Wthby. Mag. It spit a 55-grain bullet 200 fps slower than the .220 Swift not-magnum.
The term “magnum” is used rather loosely. The word itself is Latin for “great,” and before ammo makers glommed onto it, wine sellers were using it to denote a double-sized bottle of sour grapes. But do you suppose a magnum cartridge then uses a double volume of powder? Not a chance. Double performance? Not another chance. You can stuff 59 grains of IMR7828 behind a 150-grain bullet in a .280 Rem. to get 2,990 fps; 68 grains of IMR7828 behind the same bullet for 3,162 fps in the 7mm Rem. Mag.; and 87 grains of IMR7828 in the 7mm Rem. Ultra Mag. for 3,340 fps. Incremental speed increases at best. Energy levels increase more significantly, but gross foot-pounds of kinetic energy carried by bullets is highly overrated and largely superfluous.
So what really makes a magnum a magnum? Semantics. Whoever creates a round gets to name it whatever he likes. If he thinks adding MAGNUM will increase interest, it’s a magnum. Thus we have the 7mm Rem. Mag. that takes a velocity back seat to the 7mm STW non-magnum. We have the ordinary 22-250 Rem. that outshoots the .222 Rem. Mag.
Various .30-caliber cartridges. Left to right: .30 AR, .30-30 Win., .303 Savage,
.300 Savage, .30 T/C, .308 Win. The .30-06 is dead center and to its right
are the magnums: .300 H&H Mag., 300 Win. Mag., .300 WSM,
.300 Wthby. Mag., .300 RUM, .30-378 Wthby. Mag.
Handgun ammo seems to come a bit closer to what you’d expect from magnum terminology. The old .38 Special brass was just lengthened to create the .357 Mag. The .44 S&W Special was stretched to become the .44 Mag. The .454 Casull is essentially a longer, stronger .45 Colt case. The Casull was originally to be called the .454 Magnum.
Regardless of how and why magnums are designed, they are assumed to offer increased power and/or velocity over “standard” (another loose term) cartridges. Before drooling after a magnum, however, the wise shopper will research its ballistics (ammunition catalogs and websites are a good start) and compare them against other cartridges, including those without the MAGNUM moniker. Then, and only then, will he/she be properly prepared to make an informed choice.