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CLASSIC AFRICAN CARTRIDGES
Mini Compendium of
Big Bore Cartridges
Part Two of a Three Part Series
The .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
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 2300 feet per second, creating a very deadly dangerous
game round.
by Daniel McCarthy
In part one of this series we considered the .450 to .500 calibre
rounds and suitable rifles. We now continue up the scale.
A big bore lineup (from left to right): .375 H&H, .505 Gibbs, .500 Nitro Express, .500 Jeffery, .500 A-Square,
.550 Express, .550 Magnum, .585 Nyati, .577 Tyrannosaur, .600 Nitro Express, .600 Overkill, .700 Nitro Express.
VI
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 3.30 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 2100 f.p.s. from surplus
military Mauser 98 actions.
The .550 Magnum and .550 Express have an uncommon bore 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 several premium bullet makers interest and in supplying
this cartridge, and Hawk bullets are already in production. Properly
headstamped brass is available from Quality Cartridge. Alternatively
the reloader can just neck up and fireform 460 Weatherby brass.

CLASSIC AFRICAN CARTRIDGES
Barrels for the .550 Magnum are available from Dan Pederson of Cutrifle
Barrels (www.cutrifle.com) in Prescott, Arizona. Gunsmith Michael
Scherz at Gila River Gunworks, Yuma, Arizona is building barreled
actions and complete rifles for the .550 Magnum and .550 Express for
all interested customers.
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. However, at this time the .550 Magnum and .550 Express are
only suitable for the reloader.
Example ballistics:
Cartridge Bullet Velocity Notes
550 Magnum 700 grain 2300 f.p.s. Long version for CZ550 and Ruger RSM actions.
550 Magnum 650 grain 2400 f.p.s.
550 Magnum 600 grain 2500 f.p.s. Low sectional density – not preferred.
550 Express 600 grain 2400 f.p.s. Short version to fit in .458 Win. Mag. sized actions.
550 Express 650 grain 2200 f.p.s.
550 Express 700 grain 2100 f.p.s.
The .577 Nitro Express
The .577 NE 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.
The cartridge has a few downsides, however. The first is that the recoil
is rather fierce. The second is that rifles built for this calibre (other than
unsuitable single shot conversions) are as expensive as a 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 calibre 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 (www.ferlachguns.com) and Heym make bolt action
rifles in this caliber.
Sample load data for the 577 Nitro Express 3 inch is as follows:
Cartridge Powder Primer Bullet Velocity
577 Nitro Express 3” 145.0 grains IMR4831 F215 750 Woodleigh
577 Nitro Express 3”
Notes
135.0 grains Reloader 15* 750 Woodleigh 2050 f.p.s.
*Filler may be needed to avoid hangfires.
The .585 Nyati
The .585 Nyati was designed by writer and professional hunter Ross
Seyfried in order to offer the power of the .577 NE 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 NE 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 NE 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.
VII
The biggest in a small package.
A .458 Win. Mag. (left)
compared to a .550 Express
cartridge (right). The .550
Express will fit into a standard
magnum action (3.30” overall
length), making it a suitable
conversion for a rifle in .338
Win. Mag. or .300 Win. Mag.
But it will push a 700 grain
bullet at 2100 f.p.s., giving the
shooter a lot of bang for his
buck.
From left to right, .500 A-Square,
.550 Express and .600 Overkill. The
.500 A-Square and 550 Express are
very easy and economical conversions
to perform on a CZ550 in .416 Rigby.
Little more than a new barrel and
bedding are needed, with very minor
rail and ramp adjustments. A CZ550
is also very easy to convert to .600
Overkill if it is sent to American Hunting
Rifles where a single stack magazine
box is installed that feeds fast and
slick. For shooters looking for
something big and easy, these three
are the way to go.
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

CLASSIC AFRICAN CARTRIDGES
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 labour cost of doing so will be significant.
Example loads:
Cartridge Powder Primer Bullet Velocity
1 585 Nyati 2.8” 130.0 grains Reloader 15 F215 750 grain TCCI solid 2250 f.p.s.
2 585 Nyati 2.8” 120.0 grains IMR4350 F215 750 Woodleigh 2050 f.p.s.
3 585 Nyati 2.8”
Notes
90.0 grains H4831 F215 1200 grain cast 1300 f.p.s.
1 This is the author’s recoil limit.
2 Approximates .577 Nitro Express factory load.
3 Low recoil practice load.
.577 Nitro Express double rifle by B. Searcy & Co. Searcy rifles combine
traditional design, state of the art manufacturing technology, and
attention to fine detail to provide the customer with excellent dangerous
game rifles at reasonable prices.
.585 Van Horn built on a Granite Mountain Arms action by Ryan Breeding.
VIII
The .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 NE.
Although the .577 Tyrannosaur can be loaded down to reduce its
horrendous 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.
Example loads:
Cartridge Powder Primer Bullet Velocity
577 Tyrannosaur 170.0 grains IMR4350 F215 750 solid 2480 f.p.s.
In the Third and final part we will consider the .600 and up.
WARNING - Hand loading is potentially dangerous - The loading data and methods contained in this article are offered as a reference only, and relates
to an individual's weapon and experience. While it may be safe in that weapon, it may not be in others. Neither the author, nor Mag-set Publications
(Pvt) Ltd. or their agents and/or representitives are responsible for the use or abuse of this data, or the consequences thereof.