The .577 and .600 Nitro Express cartridges are well over a century old. For obvious reasons--weight, cost, recoil--neither became as popular as several lighter cartridges. However, these "ultra large bores" had their proponents, and serious ivory hunters used them in the great old days of serious ivory hunting.

One of the proponents of the .600 Nitro Express was once asked why it was his choice. Whether legend or fact, history records his answer as, "Because they don't make a .700."

In the 1980s, American hunter Bill Feldstein decided to fix this clearly vexing problem, commissioning Holland & Holland to build him a .700 Nitro Express. Whether genuinely practical or a pure curiosity, both rifles and cartridges remain rare and expensive, but since 1990 half a dozen gun makers have produced at least one .700 Nitro Express rifle, for a world population probably somewhere between 12 and 20 total rifles.

So, today, the world's biggest and baddest sporting rifles are chambered to .577 3-inch, .600 and .700 Nitro Express cartridges. I agree that, thanks to its high velocity, the .460 Weatherby Magnum produces more energy than the .577 or .600. Clearly, though, it doesn't come close in bullet weight or caliber.

There are also some really amazing wildcats out there as well, combining the caliber and bullet weight of these old double-rifle cartridges with the higher pressures that a bolt action can handle. Some that I know about include the .577 Tyrannosaur, .585 Nyati and the .600 Overkill.

There are undoubtedly others I don't know about. But since this is my story, I'm going to stick with the Big Three of Nitro Express cartridges: the .577 3-inch, .600 and .700. None of the three are common, and all are expensive (both rifles and ammo). I am certain that none of us actually needs any of them--but, whether essential or not, they are fascinating.

The imposing size of these cartridges is, well, impressive, but their paper ballistics aren't boring. And while all three cartridges have been chambered in single-shots--and both the .577 and .600 have been chambered in slant-box bolt actions--they were designed for use in doubles, so there is really just one bullet weight and one load for each.

The traditional load for the .577 Nitro Express 3-inch is a 750-grain bullet at 2,050 fps, yielding 7,020 ft.-lbs. of energy. The .600 is bigger, heavier and slower: a 900-grain bullet at 1,950 fps for 7,600 ft.-lbs. of energy. The .700 steps up to a 1,000-grain bullet, propelled at 2,000 fps, with an energy yield of 9,050 ft.-lbs. Wow.

I go back a ways with the .577, the oldest and most popular of the three. Recently, however, I had the opportunity to shoot all three and actually see them used in the field. What I'm going to give you is neither scientific nor definitive. Rather, these are my impressions of where these mighty cartridges actually fit in--if they do at all.