Big Bore Cartridges


AH elite
Sep 3, 2009
Reaction score
Member of
Tanzania, Nepal, Canada,
Big Bore Cartridges
by Daniel McCarthy


.577 Nitro Express

Goliaths of the Hunting World
Not for more than 100 years has there been such a surge in interest in big bore cartridges as there is today. This interest is fueled at least in part by the relative affordability of hunting game for which big bore cartridges are suitable. Such game is generally limited to thick-skinned dangerous game, namely cape buffalo, elephant, hippo on land, and white rhino. For half the cost of a typical new car, we can hunt cape buffalo and plains game. Trophy bull elephant can be hunted in several countries for less than the cost of a new truck, and rhinoceros can be hunted in South Africa for the same budget.

It is not necessary to be wealthy or even a high-income earner in order to afford dangerous game hunting in Africa. By scrupulously setting money aside and making a few personal sacrifices to cut expenses, such as giving up eating at restaurants, not buying tickets to professional sporting events, avoiding new or expensive cars and trucks, and by turning some of part of a gun collection into cash, almost every American wage earner will be able to afford a dangerous game hunt in Africa.

With the relative financial accessibility of thick-skinned dangerous game hunting comes a natural interest on the part of the sportsman in rifles and cartridges appropriate for that sport. Although none of us would suffer if our thick skinned dangerous game hunting were to be done exclusively with the 416 Rigby, 458 Lott and 470 Nitro Express, there is added excitement to shooting the largest and heaviest of bullets. But there is even more good news for the big bore fan. Prices for newly produced double rifles are at an all-time low with several fine offerings from Searcy, Heym, Merkel, Krieghoff and Sig coming in at around US$10,000. For a similar amount, a very nice big bore bolt rifle from several master craftsmen may also be acquired. Alternatively, there are some low-budget options for the big bore fan, which will result in a very functional big bore dangerous game rifle for about US$3000.

This article provides the reader with a summary of both factory and wildcat cartridges .50 caliber and larger that are suitable for use on thick skinned dangerous game. As a beginning proposition, cartridges that use bullets with a sectional density of less than .300 or which cannot achieve a velocity of close to 2000 f.p.s. have been omitted due to the inadequate penetration that results from those ballistics. These criteria require me to rule out any discussion of lever action cartridges and any discussion of 2 bore, 4 bore, 8 bore, 10 bore and 12 bore rifles. Although such guns may be fun projects, their poor penetration precludes them from serious consideration in a practical dangerous game rifle. Also, energy figures are not provided in this article because they are misleading. Thick skinned dangerous game do not seem to be much affected by the energy of the cartridge they are shot with, so it would be error to conclude that one cartridge would be more effective than another based solely on energy figures. Rest assured that all of the cartridges discussed in this article have plenty of power for dispatching elephant, buffalo or whatever else is on license. Just about any cartridge can be used to kill a cape buffalo with a properly placed broadside lung shot, as the tens of thousands of buffalo fallen to AK-47 rifles have proven. But stopping an enraged bull or penetrating to his vitals from a poor angle can test the limits of any cartridge. Elephant provide an even more difficult penetration challenge since a frontal brain shot on an elephant will require puncturing several feet of trunk and skull bone before the brain is reached. Likewise, buffalo shoulders and jawbones, and buffalo and elephant skulls are notorious for ruining bullets, so only quality monolithic solids or other premium nonexpanding bullets should be considered by those with an inclination toward self-preservation.

Each cartridge summarized below is discussed primarily from the point of view of building an affordable bolt-action rifle to use for thick skinned dangerous game hunting. Example loads and ballistics are shown. The nitro express cartridges are discussed for comparison purposes, even though they are typically available only in more expensive double rifles (the Heym and Hambrush bolt rifles being notable exceptions). I hope that all readers will have the chance to build or purchase a big bore rifle and hunt dangerous game with it, or at least be deterred by the mistakes of those of us who have.

505 Gibbs
The 505 Gibbs was designed by George Gibbs of London to provide big bore stopping power in a Mauser style bolt-action rifle. It is considered the king of the classic big bore cartridges and is gigantic in its dimensions. The actions that will properly handle the cartridge are gigantic as well, and the price tag for a rifle in this caliber has a Texas-sized price tag.

The 550 Gibbs has an overall length of 3.85 inches, making it unsuitable for all but a few magnum actions. Those considering a .505 Gibbs would do well to use an action that has a bolt body diameter of more than 0.700" (which is standard in the model 70/model 98/ CZ550) because after the bolt face is opened up for the Gibbs 0.640" rim, there is just a very thin sliver of metal left on the bolt opposite the extractor. Starting with a larger diameter bolt at the outset, such as the 0.750" bolt found in Granite Mountain Arms magnum mauser actions, adds to the durability of the rifle. Another alternative is a P14 Enfield action since the P14 bolt has a left lug that extends beyond the boltface, providing extra metal opposite the extractor which can accommodate the Gibbs very large rim.

At first glance, the .505 Gibbs original factory ballistics of a 525 grain bullet at 2300 f.p.s. do not appear to offer much more power than a .458 Winchester Magnum. After all, it is just 25 more grains of bullet weight and 150 feet per second more velocity. However, the ballistics can be improved by stepping up to a 600 grain bullet at 2400 feet per second. Of course the Gibbs also has the advantage of greater bullet diameter than the .458.

At present, factory 505 Gibbs rifles are available from Reimer Johannsen (, Hartmann & Weiss and Heym (Heym bei Frankonia). CZ has announced that it will introduce a .505 Gibbs rifle at the Shot Show in 2005. Alternatively, master gunsmith Ryan Breeding of Palmdale, California (Page 1) offers a beautiful 5 shot .505 Gibbs bolt rifle, and custom gunmaker Joe Smithson of Provo, Utah turns out perfection in a 505 Gibbs on a Granite Mountain Arms action. Karl-Heinz Ritterbusch ( offers top quality .505 rifles as well.

Most 505 Gibbs rifles made today are custom built by individual gunsmiths today with about a 1-2 year lead-time. It is a magnificent classic cartridge with wonderful stopping power. For those who wish to maximize the punch of a hunting rifle, even more potent combinations are discussed further below. Recoil from the .505 Gibbs is significant due to the heavy powder charges it uses. To control recoil, .505 Gibbs rifles should weigh 11 pounds or more.

On cape buffalo, the .505 Gibbs has been observed to have significantly more shock effect than anything in the .458 class, due to its greater bullet diameter. Performance on game of the .500 Jeffery, .500 AHR, and 500 A-Square will be essentially the same as the .505 Gibbs. The advantage of the .505 Gibbs is its classic design and standard dimensions without a rebated rim. The disadvantages include need for a very expensive magnum mauser action, periodic shortages of brass, sometimes inconsistent brass quality, and a relatively narrow selection of bullets for the .505" diameter bore. If you want a 505 Gibbs, there is no inexpensive route. But a well-made 505 Gibbs is a rifle is a genuine treasure.

500 Nitro Express
The predecessor to the 500 Nitro Express was the 500 Black Powder Express, but the two cartridges have radical differences in power. While the 500 Black Powder Express fired a 440 grain lead bullet at 1500 feet per second, the 500 Nitro Express fires a 570 grain bullet at 2150 feet per second. Persons coming into possession of a 500 Black Powder Express should use care not to inadvertently shoot 500 Nitro Express ammunition in it or the rifle will be ruined. Further, the 500 Black Powder Express is a good rifle for pigs, black bear and plains game, but does not have a place hunting thick skinned dangerous game, although the 500 Nitro Express is a very potent dangerous game cartridge. To add further confusion to the mix, the 500 Nitro Express comes in 3 inch and 3 1/4 inch versions. The 3-inch version is more popular, and the ballistics of the two are identical.

At the present time, double rifles in 500 Nitro Express are currently made by Heym, Krieghoff, Merkel, Searcy, Westley Richards, Sig, Rigby, Holland & Holland and others. Bolt action rifles in 500 Nitro Express are made by Hambrusch Hunting Rifles. In years past, Heym also made bolt-action rifles in 500 Nitro Express.

In double rifles, the 500 Nitro Express offers the maximum power than can be found in a rifle of reasonable weight (10-11 pounds). The more powerful double rifle calibers require a significantly heavier rifle in order to keep recoil at a manageable level. The 500 Nitro Express is also known for being able to reach the lungs of a cape buffalo if he is shot up the tailpipe. The 577 and 600 Nitro Express cannot match this penetration. The reader should note that the 500 Nitro Express has the least impressive ballistics of any cartridge mentioned in this article, although the 500 Nitro Express is actually a larger and more powerful cartridge than most professional hunters use for backup when on safari. Hopefully that will help put the awesome power of some of these cartridges into perspective.

500 Jeffery
The 500 Jeffery is misnamed as it was designed in Germany under the name "500 Schuler". Hostilities between England and Germany during the first world war resulted in British firms calling the cartridge the 500 Jeffery instead, although the two cartridges are one and the same. The European designation for the cartridge is 12.7 x 70 mm.

The 500 Jeffery is an excellent big bore stopping rifle pushing up to a 600 grain bullet at 2400 feet per second with proper reloads. Original ballistic were a 535 grain bullet at 2400 feet per second. Lengthwise penetration on buffalo using a 500 Jeffery is reported by Jaco Marais of South Africa. Similar performance can be obtained from the 505 Gibbs
and 500 A-Square.

The 500 Jeffery has a cartridge overall length of 3.45" which permits it to be built on smaller actions such as standard Mauser 98. Before the reader becomes enthusiastic about rebarreling a surplus model 98 Mauser to 500 Jeffery, there are some difficult problems to consider. First, the 500 Jeffery has a rebated rim, which can lead to feeding problems if the rifle is not properly assembled. A few master rifle makers can get a 500 Jeffery to reliably feed from a staggered magazine. Others will prefer to use a single stack Schuler style magazine for its reliability. The original Schuler rifles used a single stack magazine. Another feeding trick is to use a U-shaped follower rather than a standard L-shaped follower in order for the cartridge to ride as high as possible to avoid the bolt overriding it and closing on an empty chamber. Second, the 500 Jeffery is a fat little cartridge that will require construction of a new magazine box and extensive work to the rails and ramp of the rifle. When these issues are considered, the 500 A-Square on a CZ550 action begins to look like a much more attractive option for the budget-minded. If the reader is seeking a high end rifle in 500 Jeffery, then a true specialist at getting such a rifle to feed should be employed by the project, such as Ryan Breeding or Duane Wiebe in California, Dennis Olson in Plains Montana, or Sterling Davenport in Arizona. B. Searcy & Co.

(B. Searcy & Co. The All-American Double Rifle), Sigarms (SIG SAUER), Heym, Reimer Johannsen, Karl-Heinz Ritterbusch (Jagdgewehre Ritterbusch) and Gottfried Prechtl (GOLmatic WERKZEUGMASCHINEN - Waffen Prechtl - Jagdwaffen Sportwaffen - MAUSER Magnum) offer very fine rifles in .500 Jeffery as well.

There has been some confusion about specification for the 500 Jeffery as well. It is essential to be certain that your rifle maker and your ammo maker are working from the same spec- ification. There are reports of Kynoch ammunition not properly fitting the chamber of Heym rifles in this caliber. For the reloader this is not a problem because he will simply obtain a sizing die built to his chamber's actual dimensions.

500 AHR
The 500 AHR was designed by Ed Plummer of American Hunting Rifles (American Hunting Rifles) in Hamilton, Montana. It is intended to push 535 to 600 bullets at 2400 feet per second to duplicate the ballistics of the 500 Jeffery but without a rebated rim. AHR makes custom rifles in 500 AHR using the CZ550 action. The 500 AHR is what the 500 Jeffery should have been. An even more practical alternative is the 500 A-Square because the brass is more readily available.

500 A-Square / 510 Wells
The 500 A-Square was designed by Art Alphin of the A-Square Company ( for maximum penetration and shock power on dangerous game. Pushing a 600 grain bullet at 2400 f.p.s., the 500 A-Square is everything that a bolt gun afficianado could want. It uses a 460 Weatherby case necked up to .510" and slightly improved. The 510 Wells preceded the 500 A-Square by well over 20 years and was designed by Fred Wells of Phoenix, Arizona. Ballistics for the two cartridges are identical and selection of one over the other is merely a matter of personal preference. The 500 A-Square has a cartridge overall length of 3.75" and due to length will only fit into relatively large actions such as the CZ550. Some may be tempted to rebarrel a Weatherby Mark V or a Sako TRG to 500 A-Square thinking it a cheap and easy route to a big bore dangerous game rifle. Although the debate about controlled feed versus push feed actions is best left to another article, the author would not contemplate use of a Weatherby or Sako for this purpose. Factory rifles in 500 A-Square are available from the A-Square Company of Kentucky. B. Searcy & Co. offers bolt rifles in 510 Wells, as does Fred Wells (

There are a couple of advantages that the 500 A-Square has over the 500 Jeffery, 505 Gibbs and 500 AHR. First, cheap, high quality brass in 460 Weatherby is available from Norma, and necking it up to .510" is a simple matter. In contrast, brass for the 505 Gibbs and 500 Jeffery can be very expensive and some of it can be of varying quality. Second, the 500 A-Square has a rim that fits easily onto a 0.700" bolt, making the use of expensive magnum mauser actions unnecessary. In fact, the 500 A-Square is one of the cheapest big bore rifles to build because a CZ550 in 416 Rigby can simply be rebarreled. Then the extractor needs to be tightened, and the rails opened very slightly. There are no simpler big bore conversions. Third, the 500 A-Square does not have a rebated rim, so there are no difficult feeding issues to contend with. Unless the reader insists on being a traditionalist, the 500 A-Square is probably the best choice in .50 caliber dangerous game calibers. Rifles for this cartridge should weigh at least 12 pounds.

A short version of the 500 A-Square called the .495 A-Square is available that is short enough to be build on Winchester model 70 and Mauser model 98 actions, with extensive reworking of the magazine box, rails and ramp.

Due to brass and bullet availability, the 500 A-Square is the most practical cartridge discussed in this article and should be seriously considered by anyone seeking a big bore on a budget. The disadvantage of the 500 A-Square is that it, like the 505 Gibbs, requires a very long action, making the rifle somewhat bulky.

550 Magnum
The 550 Magnum is a new cartridge designed by Neal Shirley of Yuma, Arizona that is generating a lot of excitement. It is based on the 460 Weatherby cartridge necked up to .550" bore diameter. The 550 Magnum will push a 700 grain bullet close to 2400 f.p.s. if the shooter can stand behind the rifle.

By basing the 550 Magnum on 460 Weatherby basic brass, the historic problems related to rebated rims and/or brass of questionable quality in the 500 Jeffery, 505 Gibbs, 500 AHR and .585 Nyati are eliminated. The round will fit into a CZ550 action economically and with very little modification. The 550 Magnum pushes a 700 grain bullet at 2400 feet per second, creating a very deadly dangerous game round.

A short version of the 550 Magnum called the 550 Express will fit into Mauser 98 and Winchester model 70 actions. It has a 2.65 inch case and a 3.35 inch cartridge overall length so that it will fit into any action that accommodates a .338 Win. Mag. or .458 Win. Mag. It will be a true delight to be able to push 700 grain bullets at 2200 f.p.s. from surplus military Mauser 98 actions.

The 550 Magnum and 550 Express have a unique groove diameter of 0.550", shared only by a few obsolete cartridges. Consequently the bottleneck for 550 Magnum owners is a steady supply of top quality solids for dangerous game hunting. At the time of this writing, Mr. Shirley has gotten several premium bullet makers interesting in supplying this cartridge, Alaska Bullet Works, PA Bullets, Lead Bullets | Cast Bullet Loads | 223 | Reloading | Hot Girl at, and Hawk bullets are already in production. Properly headstamped brass is available from Quality Cartridge, and Jamison International - Formerly BeLL Brass Wildcat Brass, Custom Brass, Custom Headstamped Brass, and bullets. Alternatively the reloader can just neck up and fireform 460 Weatherby brass, though it will be slightly too short, requiring the reloader to load to OAL rather than cannalure.

Barrels for the 550 Magnum are available from Dan Pederson of Cutrifle Barrels (Classic Barrel Works) in Prescott, Arizona, Bausksa Barrels, Pac-nor, and Badger barrels in the US.

For the reloader who wants a practical big bore bolt gun of maximum possible bullet diameter, the 550 Magnum is the natural choice. If you were thinking of a 500 A-Square, 505 Gibbs or 500 Jeffery but wanted a little more bullet, the 550 Magnum provides it. Even Mauser and Model 70 fans can have a low cost big bore by rebarreling to the 550 Express. Custom loaded ammo is available from Superior Ammo.

577 Nitro Express
The 577 Nitro Express chambered in modern rifles today is the 3 inch smokeless powder version that pushes a 750 grain bullet at 2050 feet per second. It is an extremely good killer while still offering adequate penetration. Rifle maker Butch Searcy reports excellent penetration and stopping power when using the .577 for elephant head shots and buffalo body shots. The cartridge has a few downsides, however. The first is that the recoil is rather fierce. The second is that rifles built for this caliber (other than unsuitable single shot conversions) are as expensive as a low-priced new car. The third is that 577 Nitro Express rifles typically weigh 13-16 pounds, and are quite difficult to carry day after day on safari. However, for the person who must have a stopper, this is definitely one of them.

There is also a 577 Nitro Express 2 ¾ inch version. It pushes a 650 grain bullet at 1850 feet per second. Coming up short in both sectional density and velocity, penetration with this caliber will not be satisfactory on the more difficult head shots on elephant or quartering away shots on buffalo. There was also a 577 Black Powder Express which pushed a 520 grain lead bullet at 1700 feet per second. Those rifles, while fun novelties and great for pigs and cats, should not be considered an appropriate choice for thick skinned dangerous game.

Various double makers, including Searcy, Westley Richards, Holland & Holland and Heym make double barreled rifles in 577 Nitro Express. In addition, Hamrusch (Hambrusch Hunting Weapons - Jagdwaffen Ferlach - Used Guns - Barrels - Gebrauchtwaffen) and Heym make bolt action rifles in this caliber.

585 Nyati
The .585 Nyati was designed by writer and professional hunter Ross Seyfried in order to offer the power of the .577 Nitro Express cartridge in an affordable bolt action rifle. At the time when Mr. Seyfried designed the cartridge, double rifles were out of the financial reach of most professional hunters and client hunters alike, so the concept of bringing the tremendous stopping power of the 577 Nitro Express to a bolt action rifle had great allure. Today one of the most affordable double rifle makers is B. Searcy & Co.of Boron, California, but even there a 577 Nitro Express double will cost US$15,000 at the time of this writing. In contrast, a well-planned low grade .585 Nyati bolt gun can be put together for only US$3000. The author had such a rifle constructed on a Winchester model 70 action built by gunsmith Franz Bryner of Ogden, Utah.
The disadvantage of the .585 Nyati is its use of a rebated rim so that rifles with a 0.700" bolt body diameter can be fitted for the cartridge. It can be difficult to get a rifle using a cartridge with a rebated rim to feed reliably (see discussion of 500 Jeffery above), so a project for this cartridge should only be undertaken by a master big bore specialist, or by someone who is willing to experiment and throw away the action if unsuccessful.

The standard .585 Nyati uses a 0.640" rim and has a case length of 2.800". Another variation uses the same rim but a 3.00 inch length case. With its greater powder capacity, the 3 inch version can push a 750 grain bullet even faster than the 2500 feet per second achievable by the 2.8 inch version, but to what useful end the author cannot imagine. A third variation uses a 0.590" rim (same as the 416 Rigby) to avoid the use of an expensive action with a bolt body diameter of greater than 0.700" which would be desirable on the 0.640" rim version. However, with the severely rebated 0.590" rim, reliable feeding is an almost unobtainable goal so the reader is encouraged to avoid this variation. A ballistically identical cartridge called the .585 African Express (Ralston) has been designed by Brad Ralston of South Africa. It uses a full sized rim instead of a rebated rim for use in the Granite Mountain Arms magnum mauser action. The .585 Van Horn also offers similar ballistics with some variations in case dimensions.

Another issue with the .585 Nyati is that many barrels are being produced with excessively tight chamber necks. The author believes this may be due to an error in original drawings for the cartridge. If your barrel maker sends you a barrel with a tight neck, just ream it out to 0.614" with a neck reamer and tight necks (and dangerous pressures) will not be a problem. Rifles for the .585 Nyati cartridge should weigh a minimum of 11 pounds and preferably 13 pounds in order to make them controllable. For hunting purposes, the owner of a .585 Nyati should consider keeping his velocities below 2300 feet per second or follow up shots will be slow.

The author has used the .585 Nyati on elephant and buffalo with satisfactory results. Both were heart/lung shots at under 25 yards, and in each case the game traveled less than 20 yards before collapsing. The buffalo was spooked before being shot, but his adrenaline was no match for a 750 grain solid moving at 2250 feet per second. The recoil is violent and always surprising. I can shoot 10-14 shots of .585 Nyati in a day, but only if I take Tylenol before going to the shooting range.

At present I know of no factory rifles in .585 Nyati nor are there likely to ever be any. Rifles in this cartridge are strictly a custom affair, and ammunition should only be loaded by the advanced reloader. Although the .585 Nyati is a very effective and fun cartridge, it is not very practical. Brass can be of inconsistent quality and/or in short supply. Only big bore experts are likely to get a rifle in this cartridge to feed properly, and the labor cost of doing so will be significant.

577 Tyrannosaur
In the days that the British ruled most of huntable Africa, the magic velocity for dangerous game hunting was considered to be 2150 feet per second. During the past 30 years the game has changed, however, and sportsmen demand ever more from their rifles. Now in order to assure adequate penetration from every angle, the conventional wisdom is that a cartridge should generate 2400 feet per second.

The 577 Tyrannosaur is a modern day attempt to blend the giant .585 diameter 750 grain bullets of the 577 Nitro Express with the magic velocity of 2400 feet per second. The result is a brutish rifle that is nearly uncontrollable. Another consideration is that monolithic solids should be used in this cartridge because bullets of a convention design meant for 577 Nitro Express velocities will likely rivet or break apart at 577 Tyrannosaur velocities. One Norwegian hunter shot an elephant in the spine using a .577 Tyrannosaur loaded with Woodleigh 750 grain solids. The Woodleigh riveted and fishtailed, as it had been pushed beyond its design criteria.

For the sportsman interested in building a custom rifle for the 577 Tyrannosaur, only a magnum length (3.800") magazine box will suffice, thus ruling out model 70's and Mauser 98's. Further, the enormous diameter of the case rim (0.688") requires either a P14 Enfield bolt, or at least a 0.750" bolt body diameter. Magazine box and follower construction as well as rail and ramp modifications to the action will all be completely custom and should only be attempted by the most skilled big bore specialist. Brass and ammo for the 577 Tyrannosaur are even more expensive and harder to find than for the 577 Nitro Express. Although the 577 Tyrannosaur can be loaded down to reduce its horrendous and almost uncontrollable recoil, the .585 Nyati would be a better choice for lower velocity loads since it burns less powder and therefore will produce less recoil. Factory rifles in .577 Tyrannosaur are available from the A-Square Company of Kentucky. Custom gunsmith Joe Smithson of Provo, Utah offers fine custom rifles in .577 Tyrannosaur based on the Granite Mountain action.

600 Nitro Express
The .600 Nitro Express was designed by Jeffery in 1903. There was no black powder predecessor to it. It fires a 900 grain bullet at 1950 feet per second, although in Jeffery double rifles it was regulated for 1850 f.p.s. At these somewhat anemic velocities, the cartridge never developed a reputation for being a deep penetrator. Further, there were some reports of bullet failure with the old Kynoch bullets which had a thin copper jacket and were subject to riveting. Modern solid bullets from Woodleigh include a steel liner inside their jacket that enhances their durability, and Barnes offers a monolithic brass solid in this caliber. The Woodleigh solids have a very blunt shape intended to impart the greatest possible shock to an elephant's head.

The idea behind the .600 Nitro Express was to provide a cartridge that will deliver a tremendous shock to a wounded elephant so that if the hunter missed the brain, the shock from the bullet would still knock the animal down. John Pondoro Taylor reported elephants head shot with the .600 Nitro Express when the bullet missed the brain remaining unconscious for up to 30 minutes. While I doubt the sanity of a man who would measure the time it takes an unconscious elephant to awaken and resume his charge, the recoil of the .600 Nitro Express is convincing enough to the shooter.

Rifles in .600 Nitro Express are typically doubles, making them rather expensive. Searcy Enterprises offers a .600 Nitro Express boxlock double for US$25,000 as of this writing, and Heym offers one for US$38,000. Other makers are in the game too, but from there the prices go up. Bolt-action 600 Nitro Express rifles are available from Heym Waffenfabrik in Gleichamberg, Germany for only US$13,000. Bolt action rifles in .600 Nitro Express are also available from Hambursch Hunting Guns in Ferlach, Austria.

The author owned a Heym Express Rifle in 600 Nitro Express and found it extremely well made and well balanced, and capable of putting 3 shots into 3 inches at 50 yards from an offhand position. However, the recoil was so great that the rifle was pointing upwards at a 70 degree angle after each shot, and the author needed to rest 10 minutes between shots to get over that 'car accident feeling'. Other than that minor inconvenience and the great weight of the rifle, my 600 Nitro Express was a delight. I wish I had owned the same rifle in a .50 caliber cartridge. In the end, however, I had to decide whether to leave a large block of cash tied up in the Heym or go elephant hunting. Elephant hunting won, and the Heym found a new residence.

In reality the .600 Nitro Express is not a practical choice due to its weight, cost, recoil, and somewhat shallow penetration. The reader would be better off to consider a .550 Magnum or 500 A-Square instead. In a double rifle, a 500 Nitro Express is more practical.

600 Overkill
The 600 Overkill was designed by scientist Robert Garnick of Las Vegas, Nevada. It was intended to take full advantage of the dimensions of the CZ550 action in order to fit into that action the largest cartridge that could be accommodated. With moderate alterations, a CZ550 can be made to accommodate 2 cartridges of 600 Overkill in the magazine plus one in the chamber. Using brass solids bullets, the 600 Overkill will penetrate 6 feet into an oak log. Even elephant skulls are not as dense as oak, assuring that the 600 Overkill pushing 900 grain solid bullets at 2400 f.p.s. will offer excellent penetration on any game.

The 600 Overkill case originated from the 600 Nitro Express. The rim was removed from the 600 Nitro Express and a belt was added for headspacing purposes. A 0.640" rebated rim was cut on the case - the same size used by the .505 Gibbs. The case walls were left straight for a 3.0 inch case and a 3.75 inch cartridge overall length. Custom 3 groove barrels with 1:16 twist are made by Pac-Nor Barrels of Brookings, Oregon. A 3 groove barrel with a 1:16" twist was chosen to keep pressures low and permit the cartridge to achieve higher velocities than would be otherwise possible. This scheme seems to have worked because with the same powder charge and bullet, the 600 Overkill achieves about 75 f.p.s. more velocity than the 600 Nitro Express.

The 600 Overkill has the ability to push a 900 grain bullet at more than 2400 f.p.s. if the shooter can withstand the recoil and maintain his grip on the gun. At that level of power, as the bullet spins down the barrel, the rifle is torqued in the opposite direction, tending to twist the forearm of the rifle out of the shooter's hand. Brass for the 600 Overkill is available on a special order basis from Dieter Horneber ( of Germany. Rifles may be ordered from American Hunting Rifles for not much more than US$3000. For the big bore fan who needs the biggest affordable big bore, the 600 Overkill based on a CZ550 action is for him.

700 Nitro Express
The 700 Nitro Express came about when a customer of Holland & Holland wanted to purchase a 600 Nitro Express double rifle, but H&H had sold the "last one". Undaunted, the customer pushed the project ahead and H&H built a 700 N.E. double rifle for him. Currently H&H, Watson Bros. and Searcy Enterprises offer double rifles in 700 N.E. Hambrusch Hunting Weapons of Ferlach, Austria offers a bolt-action repeater in 700 N.E. as well. Standard ballistics indicate a 1000 bullet at 2000 f.p.s. However, there has been some discussion of penetration problems with the cartridge and talk of increasing the bullet weight to 1200 grains while keeping velocity at 2000 f.p.s. to improve penetration. Rifles for this caliber weigh in the 16-20 pound range and only the fittest of men can carry such a burden for 20 miles on an elephant track in the hot African sun.

A 700 Nitro Express was taken on a recent elephant hunt in Botswana with Safaris Botswana Bound (, and the following report was provided by Graeme Pollock.

"The gun was too heavy for the hunter to walk the long distances sometimes required in Elephant hunting…. The first shot on the Elephant was a frontal shot which did not hit the brain and did not knock the Elephant down. The shot was apparently high due to a hang fire. The second shot was lung heart and the elephant again did not go straight down but it did not move much either before going down. The 1000g bullet seems to have not much more noticeable knockdown power than the 500 or 470 NE 500g round."

Similarly, professional hunter Mark Sullivan who has hunted with a 16 pound Watson Brother's 700 Nitro Express, finds it a bit too heavy to get onto charging buffalo as quickly as he would like. When considering the cost of a rifle in 700 Nitro Express, the weight and difficulty of carrying one, and the savage recoil, the performance on game is rather disappointing.

For the person wanting the biggest bolt action dangerous game rifle that there is, the Hambrusch .700 NE has no competition. A more affordable alternative with nearly as large a bore diameter is found in the 600 Overkill, which can be constructed for a little more than US$3000 using a CZ550 action. Most rifles fall between these two extremes and at this time an excellent big bore bolt action rifle suitable for use on dangerous game can be built for between US$10,000 and US$20,000.

Some of the more practical alternatives for the reloader seeking maximum power are found in the .550 Magnum, .550 Express, 500 A-Square and 495 A-Square which are all based on .460 Weatherby brass which is plentiful and relatively inexpensive. For the traditionalist, a 505 Gibbs is an option and it is certainly attractive in some of the fine rifles that are available. A .500 Jeffery, when assembled by a expert big bore riflemaker, is also a sound choice. The other cartridges each have their place, depending on the shooter's preferences. No matter which of these the reader may choose, I can assure you that the .375 H&H will have absolutely no felt recoil after a range session with your new big bore.

The "EMPEROR" .375 H&H Magnum Rules...
Last edited by a moderator:
Always love reading about the big bores!!
I guess at the end of the day, it depends on how effectively you can handle one of these "monosters". If you can should be great catridges.
Nice read but for my 160lbs I think I'll keep everything under a .458 Win Mag. just reading this made my shoulder hurt.
11 pounds sounds light…


  • Screenshot 2023-09-15 at 7.52.28 AM.png
    Screenshot 2023-09-15 at 7.52.28 AM.png
    1.5 MB · Views: 45
  • Screenshot 2023-09-15 at 7.52.30 AM.png
    Screenshot 2023-09-15 at 7.52.30 AM.png
    2.4 MB · Views: 52

Forum statistics

Latest member



Latest profile posts

T/C wrote on Dewald's profile.
Hi Dewald,
I am looking for a copy of Wright's "Shooting the British Double Rifle" (3E).
Please PM me (T/C) if you still have one.
Thank you very much in advance!!!
I am game for a meat and eat. My attempt at humor.
rigby 416 wrote on rifletuner's profile.
Come from cz like that.
John A Flaws wrote on Horbs's profile.
500 schuler magazine.jpg
500 schuler bore.jpg
500 and 425 rifles.jpg
500 and 425 magaizne.jpg