WHAT, EXACTLY, IS A MAGNUM?
WHAT, EXACTLY, IS A MAGNUM?
I J Larivers
We are all familiar with the term “Nitro Express”, and we understand it to mean a series of calibres that were designed for use in the big-bore hunting rifles. These cartridges are especially associated with African big game hunting, the age of the Great White Hunters, and all that good stuff. In actual fact, they were named for the new propellant they used - Cordite - which comprises nitrocellulose and nitroglycerine, and for the high speed express trains of the day. James Purdey coined the term in 1856 as a marketing ploy for his fine double rifles. Many of the NE cartridges survive into the 21st century, notably the .470NE and the.600 and .700NE.
These Nitro Express rounds were the magnum cartridges of their day. But just what is a “magnum”? The word is commonplace in modern lexicon, thanks in great part to television and the movies. It is commonly defined as “A thing of a type that is larger than normal”, and has been applied to everything from cartridges to champagne bottles.
When I was growing up in the ‘60s and ‘70s a much sought-after thing was any offering in .22 magnum. This, of course, is the .22 Winchester Magnum Rimfire when it’s at home, but as kids, all we wanted was the extra power. Today, living in Zimbabwe and shooting some Olympic disciplines, I’ll kill for decent subsonic ammo like Swartklip Match Trainer or Eley Target or Club which exhibit superior accuracy. In many ways, it was great being a kid, though!
In a rifle, I understand the term magnum to mean an oversized cartridge, which, back in the day, meant more propellant and thus higher velocity; this implies that it is a “new and improved” version of a primogenitor, in the way that the .375 H&H Magnum is the top end of the 9.3mm line. The traditional magnum rifle calibres, unless rimmed for use in double rifles, also headspaced on a belt extending around the case head region, and this belt is, to many, iconic of the magnum species, to the point where some even use it as a definition.
Some purists still maintain that no belt, no magnum, but of course another whole branch of the evolutionary tree of firearms is the rise of the bolt action rifle. Since pressure is the same throughout the whole of the case, the belt does not significantly increase the strength of the case but its main purpose is allowing the cartridge to headspace properly without the danger of case head separation. Rimmed, or “flanged” cases are ideally suited to double rifles but do not feed as reliably in bolt-action models.
In 1912, during the age of colonialism and the first era of big game safaris to the Dark Continent before the Second World War, Holland and Holland brought out what is arguably the first magnum calibre, the .375 H&H. While you can see its origins in the iconic 9.3s, the .375 H&H also became a parent cartridge for other Holland and Holland offerings such as the .300 H&H Magnum, and, with a length of 2.85" ushered in the era of the long action rifle in the bolt guns. The name of the game was improved performance. (Conversely, it’s interesting to note that the original magnum calibre chambered for a handgun, the .357, now comes out in most brands of factory ammunition with a muzzle velocity almost 200fps less than originator Elmer Keith had envisaged.)
The .375 H&H was also the parent case of the blown-out .458 Winchester Magnum, which was brought out to provide ballistics similar to the venerable .450 NE, but shortened to function in a standard-length bolt action rifle. Many sport hunters and professional hunters today still swear by the .458 Win Mag, and, as evidenced by the upsurge in .458 Lotts and .458 Africans, many - especially reloaders - feel more comfortable with the longer traditional cartridge cases. When Remington introduced its .416 Remington Magnum, it did not shorten the case, but stayed truer to the .original 416 Rigby.
During the middle of the 20th century, Roy Weatherby in the United States did a lot of work with the old .300 H&H, shortening it for his .257, .270 and 7mm Weatherby Magnums, and leaving the length unchanged for his .300, .340 and .375 Weatherby Magnum offerings. All were true magnums, and gave the shooter improved ballistic performance. Weatherby’s “big guns” were the .378, .416 and .460 Weatherbys, all based on the .416 Rigby. Sadly, owing to unstable politics, on-again, off-again arms embargos, and the fact that sport shooting is not as widespread as it could be in Africa, the Weatherbys were always regarded as a couple of beats off for use in Africa - but there is no disputing their quality or performance.
This all sounds straightforward enough. Take an existing calibre, develop it to provide greater performance, and you have a magnum. The issue is somewhat complicated today by the “super magnums” and “short magnums” and “light magnums”, and “short action ultra-magnums” and “super short magnums”, but those are just the times in which we live. There are also calibres, such as the .460 Dakota which fit the bill admirably but don’t boast the moniker.
Conversely, a cartridge may be branded a magnum, like the .350 Remington Magnum, but its performance is no greater than the venerable old .30-06 Springfield-based .35 Whelen, so a magnum it is not. Not really.
What’s in a name? In 1935 Winchester introduced the .220 Swift, he brainchild of Grosvenor Watkins, which was the first commercial factory offering with a muzzle velocity exceeding 4,000fps - and it fits the magnum definition in every way. It was 1,400fps faster than its arch-rival the .22 Hornet and was also proven to be very accurate. “Hornet”? “Swift”? Both of these calibres remain popular to this day, but did they achieve as much commercial success as they could have had they been “magnums”?
“Magnum” designation is, for the most part, based on velocity. Take your parent case and increase the velocity by one or two hundred feet per second, and, all other things being equal, you will have improved the calibre’s performance. Is it worth it? Look at the .30-06 Ackley Improved. This cartridge still stirs spirited debate on a lot of forums. On the plus side, you’re going to get a hundred feet per second increase in velocity and then possibly have trouble selling a modified rifle later on. Why not just buy a .300 Win Mag? Or, of course, a .300 Winchester Short Magnum? In the 21st century there are perhaps too many choices available, if such a thing is possible.
One of the things it’s second nature to be concerned with when using velocity to improve performance is case pressure. We all know the most common signs of excessive pressure and what to look out for, and pressure testing equipment today is on the verge of finding its way into shooters’ range bags. Just what difference did magnum loads make?
Chamber pressure can either be measured in CUP (copper units of pressure) or PSI (pounds per square inch). I don’t know of any standard correlation for the two, though I stand to be enlightened. I have seen the .223 Remington rated for 52,000CUP / 55,000PSI, the .308 Winchester for 52,000CUP / 62,000PSI and the .30-30 at 38,000CUP / 42,000PSI. Apples being apples and oranges being oranges, let’s pick a unit and stay with it.
The old .470NE had a chamber pressure of around 32,000PSI back in the day, and SAAMI (the Sporting Arms and Ammunition Manufacturers’ Institute) lists it at 41,000. The .416 Rigby is listed at 52,000PSI and the .458 Win Mag comes in at 60,000PSI. The 7x57mm Mauser is rated for 51,000PSI and the 7mm Remington Magnum for 61,000PSI. As can be seen from this, “the acceptable range” is pretty much of a muchness. For those of you who have seen the excellent video posts from Accurate Reloading, the maximum average pressure for even the mighty .577 Tyrannosaur is only 60,000PSI.
Hornady embarked on an interesting journey, which only the big commercial ammo manufacturers can, because they have access to powders and reloading technologies that are specially formulated for them and beyond the scope of Everyman. They were able to achieve the improved performance through increased velocity pretty much across the board in their conventional cartridges without noticeably increasing pressures. So, having turned non-magnums into magnums, what if they applied the same processes to their existing magnums? Thus was born the “Superformance” line of cartridges. Hornady, applied the same technology to various rifle manufacturers’ proprietary cartridge lines, with boosted velocities on offer for the .300 and .338 Thompson-Center and Marlin Express calibres, and Ruger’s line of Compact Magnums.
Like never before, bullet and propellant manufacturing processes offer almost unlimited possibilities for experimentation and development. We are a long way today from the days when Cordite was king and the large case capacity “nitro express” was the cutting edge. I’m going to argue that the very concept of a “magnum” is a holdover from those days.
Much of the impetus for this kind of innovation comes from the United States, where the market is largest, and so traditional American calibres are the ones oft experimented with and written about. If you go back to the more “traditional” performance of homegrown American standbys like the .30-30 and the .444 and .450 Marlins, Hornady’s technology has virtually made “magnums” out of them too. Add in another factor - that of the bullet itself - and with Hornady’s Flex-Tips these old workhorses offer devastating performance.
By international standards, a wine bottle contains 750ml. A magnum, on the other hand, holds 1.5 litres. So, I suppose it’s only a matter of time before someone comes along and invents the .458 Jeroboam.
PHOTOS
- Pierre van der Walt's epic African Dangerous Game Cartridges: a history and a technical reference.
- An array of magnums.
- The venerable .357 and .44 magnums.
- The .270 Winchester Short Magnum, the .300 Win Mag, and the .375 H&H magnum.
- A trio of .458s: Win Mag, Lott, and African.
- The .416 Remington, the .404 Jeffery and the .470NE
- The second volume in Pierre's planned 5-volume series.
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