The .408 Cheyenne Tactical is a specialized rimless, bottlenecked,
centerfire cartridge for military long-range sniper rifles that was
developed by Dr. John D. Taylor and machinist William O. Wordman. The round
was designed with a possible military need for a cartridge for anti-personnel,
anti-sniper and anti-materiel roles with a precision range of 2,200 yards. It is
offered as a competitor to the most common military NATO long-range service
cartridges such as .338 Lapua Magnum and the .50 BMG.
History The .408 Cheyenne Tactical is based on
the .400 Taylor Magnum, which is based on a modified .505 Gibbs, necked down to
0.408 inches. The .505 Gibbs is an old English big game cartridge that was
designed to accommodate 39,160 psi pressure. One of the disadvantages to
these old cartridge cases intended for firing cordite charges instead of modern
smokeless powder is the thickness of the sidewall just forward to the web. During
ignition, the cartridge's base, forward to the bolt face, is not supported. The
case is driven back against the bolt face which results in the stretching of
the case, particularly the sidewall immediately forward of the web. When the
sidewall resists the outward expansion against the chamber, the pressure
stretches the case thereby increasing its length resulting in the sidewall
becoming thinner at that stretch point. In the .408 CheyTac cartridge casing
design particular attention was directed toward thickening and metallurgically
strengthening the case's web and sidewall immediately forward to the web
to accommodate high chamber pressures. In modern solidhead cases, the hardness
of the brass is the major factor that determines a case's pressure limit
before undergoing plastic deformation. Lapua Ltd. solved this problem when they
used the .416 Rigby as the parental case to the .338 Lapua Magnum. They created a
hardness distribution ranging from the head and web to the mouth as well as a
strengthened case web and sidewall immediately forward of the web. This
method results in a very pressure resistant case.
Cartridge dimensions The .408 CheyTac is neither officially
registered with nor sanctioned by the Commission Internationale Permanente
pour l'Epreuve des Armes à Feu Portatives or its American equivalent,
Sporting Arms and Ammunition Manufacturers' Institute. Such
cartridges are generally known as wildcats. Wildcat cartridges have no
official dimensions nor other performance related specifications.
Stated data about wildcats is always informal and using them is at one's own
risk. According to the QuickLOAD interior
ballistics predictor program the cartridge case capacity of the .408
Cheyenne Tactical is about 159 grains of water. The exterior shape of the case
was designed to promote reliable case feeding and extraction in bolt action
rifles, under extreme conditions. QuickLOAD states the maximum operating
piezo pressure at 63,816 psi and shows that this is a wildcat cartridge. The
common rifling twist rate for this cartridge is 330.2 mm for every 13 inch
the projectile travels forward through the rifled barrel), eight 0.4080 in
grooves, 0.4010 in bore 0.050" land width, square cut, no taper and the
primer type is large rifle. The .408 Cheyenne Tactical as parent
case The .408 CheyTac serves as the parent
for several other second-generation wildcat cartridges.
By blowing out .408 CheyTac factory cases the wildcatter generally hopes to
gain extra muzzle velocity by increasing the case capacity of the factory parent
cartridge case by a few percent. Practically there can be some muzzle
velocity gained by this method, but the measured results between parent
cartridges and their "improved" wildcat offspring is often marginal. An example
of a blown out .408 CheyTac variant is the .408 Baer.
Besides changing the shape and internal volume of the parent cartridge case,
wildcatters also can change the original caliber. Because the .408 CheyTac offers
a large and sturdy, pressure resistant cartridge case it has become quite
popular amongst wildcatters. With the .408 CheyTac as the parent case
wildcatters have created .338, .375, .416, and .510 caliber variants. As of
2007, the 0.375 inch caliber variants seemed to attract the most attention.
The company that designed the CheyTac Intervention rifle, CheyTac, LLC, itself
offers rifles in a .375 CheyTac chambering in their 2007 retail price
list. Projectiles
Most .408 CheyTac factory ammunition uses solid projectiles or bullets rather
than jacketed lead-core bullets, which are common to most other rifle bullets.
The oldest factory .408 CheyTac ammunition uses bullets designed by
Warren S. Jensen and originally produced by Lost River Ballistic Technologies.
Currently these projectiles are produced by Jamison International, where they are
turned on Swiss-type CNC lathes from solid bars of proprietary copper nickel
alloy. The factory claims their diameter is accurate to "one 50 millionth" but
does not provide a unit of measurement with this claim, making it somewhat
vague. One noted downside to the use of solid mono metal projectiles is that
they tend to increase the fouling left in the rifle barrel after they are
fired. Since the bullets are harder and more abrasive than the gilding metal
jackets of normal jacketed bullets, they are made slightly "undersized" so that
they may be gripped effectively by the lands of the barrel's rifling. This
inevitably reduces the seal of the bullet in the barrel, allowing hot
gunpowder gases to reach the sides of the projectile, vaporizing some of the
material and depositing it in the bore. Other manufacturers, such as Rocky
Mountain Bullet Company/Vigilance Rifles, GS Custom Bullets, Lehigh
Bullets & Design, Lutz Möller and TTI Armory have developed lead-core or mono
metal very-low-drag projectiles for the .408 CheyTac.
In 2007 Dr. John D. Taylor designed a new class of armor-piercing projectiles
is called the .408 CheyCorey and in this configuration, it outperforms the .50 AP
cartridge against armor steel and titanium. The projectile has a mass of
370 grains. Claimed penetration of AR500 certified steel is 1 inch at 100 yards
and 1/2 inch at 775 yards. In 2008 factory loaded .408 CheyTac
420-grain lead core bullets with 955 copper jackets became available. The
very-low-drag bullets are made by Rocky Mountain Bullets in Philipsburg, Montana
and have a rebated boattail and a claimed ballistic coefficient of 0.874.
Factory .408 CheyTac ammunition is expensive, starting at around $7 per
round with Jamison International 419-grain very-low-drag projectiles.
= Ballistic coefficient of the Jamison 419-grain projectile=
Cheyenne Tactical claimed a Doppler radar-measured G1 ballistic coefficient
for the Lost River Ballistic Technologies/Jamison International
419-grain bullet of roughly 0.934 and a stated BC for the 305-grain bullet of
0.611, though these numbers have been disputed by a number of knowledgeable
sources. Extreme Firearms claimed the G1 BC of the same .408 CheyTac projectile
to average 0.945 to 2000 meters and it drops to the low 0.900s to 2800 meters.
The .408 CheyTac projectile remains supersonic up to 2,300 yards according
to Extreme Firearms. CheyTac LLC claims that the 26.95 gram projectile has a
supersonic range of 2,200+ yards at 'standard air conditions'. The average
ballistic coefficient of the 419 grain is 0.945 over 3,825 yards. Jamison
International states the G1 BC of this bullet on their website currently at
0.940. The above variations can be explained by
differences in the ambient air density used for these BC statements or
differing range-speed measurements on which the stated G1 BC averages are
based. The BC changes during a projectiles flight and stated BC's are
always averages for particular range-speed regimes. Some more
explanation about the transient nature of a projectile's G1 BC during flight
can be found at the external ballistics article. This article implies that
knowing how a BC was established is almost as important as knowing the
stated BC value itself. = Balanced-flight/controlled-spin
projectile= Lost River Ballistic Technologies stated
that "the .408 CheyTac is the first bullet/rifle system that utilizes what
they call a balanced flight projectile. To achieve balanced flight the linear
drag has to be balanced with the rotational drag to keep the very fine
nose of the bullet pointed directly into the oncoming air. It should result in
very little precession and yaw at extreme range and allows accurate flight
back through the transonic region. This is hard to achieve for small arms
projectiles. Mathematically you are at a great disadvantage trying to achieve
balanced flight with a lead core non mono metal bullet. The rotational
mass/surface area ratio is too high."[2] The balanced flight projectile patent
can be found at the US Patent Office, Controlled spin projectile, US PAT No.
6,629,669. According to the patent a projectile engraved and launched in
accordance with the patent should decelerate from supersonic flight
through transonic to subsonic in a stable and predictable manner effective
to a range beyond 3000 yards. It implies that amongst several other preconditions
the rifle barrel has to have specific rifling dimensions to achieve a desired
amount of axial air drag on the bullets surface, which reduces the bullets
spinrate to achieve balanced flight. The patent does not account for normally
occurring differences in air density. More about balanced flight can also be
found in the CheyTac Information Papers. The Balanced Flight/Controlled Spin
Projectile bullet patent has been questioned/disputed by the German
physicist Lutz Möller. Mr. Möller realized balanced flight has to do with
the nature of spin stabilized flight and scale of parameters. There were
projectiles produced prior to the patent that remain stable through the transonic
flight regime. This is a consequence of the spin deceleration and forward
deceleration of the projectile being similar enough not to cause undesirable
precession and yaw during the transonic flight phase. The main parameter for
achieving stable transonic transition is controlling the drag coefficients and
forward velocity loss around Mach 1 and to a lesser degree controlling the spin
deceleration. In other words, any bullet with appropriate drag behaviour around
Mach 1 and mass will do exactly what the balanced flight projectile patent
states. Performance
The cartridge delivers accurate performance from a sniper rifle
platform. The Lost River Ballistic Technologies/Jamison International
419-grain very-low-drag bullet is the standard, long-range sniping load.
Lost River Ballistic Technologies also designed a 305 grain bullet for the
Battlefield Domination Round. The BDR is loaded with a 305 grain bullet and is
intended for short and medium range application using the point blank range
aiming method. = Supersonic range=
For a typical .408 CheyTac chambered gun, shooting 27.15 gram Lost River
Ballistic Technologies bullets at 884 m/s muzzle velocity, the supersonic
range would be 1930 m under International Standard Atmosphere sea
level conditions. For a typical .375 CheyTac chambered
gun, shooting 24.30 gram Lost River Ballistic Technologies bullets at 930
m/s muzzle velocity, the supersonic range would be 2230 m under
International Standard Atmosphere sea level conditions.
Improvement beyond this standard while still using standard .375 CheyTac brass
is possible, but the bullets have to be very long and the normal cartridge
overall length has to be exceeded. The common .375 CheyTac 292 mm rifling twist
rate also has to be tightened to stabilize very long projectiles. The use
of such a .375 CheyTac based cartridge demands the use of a custom or
customized rifle with an appropriately cut chamber and a fast-twist bore. An
example of such a special .375 caliber extreme range bullet is the German CNC
manufactured mono-metal 26.44 gram .375 Viking is calculated by its designer,
Mr. Lutz Möller, and not proven by Doppler radar measurements). This bullet
has since exhibited dynamic stability problems and is no longer produced. The
.375 Viking bullet had an overall length of 70 mm and derived its anticipated low
drag from a radical LD Haack or Sears-Haack profile in the bullet's nose
area. Rifles chambered for this wildcat cartridge, with a cartridge overall
length of 119 mm, were to have been equipped with custom made 762 mm long
203 mm twist rate barrels. In theory, Mr. Möller calculated that a
typical .375 CheyTac chambered gun, shooting his now defunct 26.44 gram .375
Viking bullets at 870 m/s muzzle velocity, would have a supersonic range
of 3090 m under International Standard Atmosphere sea level conditions.
However, field testing of this projectile proved it to be completely
unstable, and useless at any velocity, or range. This was established in
February 2009 by Terry Holstine, an Oklahoma State Trooper, who is the only
person to ever have fired the Viking. It would appear that Mr. Möller did not
test this projectile prior to public release whereby the dynamic instability
would have been discovered. The ballistic coefficient of this bullet has
never been verified, therefore the supersonic range using this projectile
cannot be determined due to the instability and unknown ballistic
coefficient regardless of the claims made.
Chambering availability The .408 Cheyenne Tactical chambering is
offered for these factory rifles: BCM Europearms S.a.s.
CheyTac Intervention rifle series - CheyTac LLC.
E.D.M. Arms XM04 PGWDTI Timberwolf .408 CheyTac and .416
PGW rifle - Prairie Gun Works Defence Technologies Inc.
Lawton Machine LLC. Lobaev Sniper Rifle
Grande Armeria Camuna precision rifles RND Manufacturing, Inc.
Tactilite T1 AR-15 .408 Chey Tac upper THOR XM408
Vigilance Rifles VR1 Desert Tactical Arms HTI
Several high quality large tactical and match custom bolt actions were designed
for the .408 Cheyenne Tactical cartridge and were becoming available as of 2007.
These semi-custom bolt actions are used with other high grade rifle and sighting
components to build custom sporting and target rifles. Such rifles are ordered
by long-range accuracy oriented shooters and built by specialized, highly skilled
gunsmiths and can cost thousands of dollars. When built to expectation such
rifles are very accurate—0.5 MOA or better consistent accuracy for a
particular rifle optimized ammunition is considered normal. Only expert marksmen
can make use of this extreme accuracy potential.
See also .505 Gibbs
CheyTac Intervention 10 mm caliber
.338 Lapua Magnum .416 Barrett
List of sniper rifles List of individual weapons of the U.S.
Armed Forces Table of handgun and rifle cartridges
References .408 Cheytac Intervention at World of
Firearms .408 CheyTac Trip Report, Shooters'
Observations and Test Results by Dean Michaelis
Barrett .416 vs. Cheyenne Tactical .408 Precision Rifle 408 Cheytac project
External links CheyTac Website
Controlled spin projectile at Google Patents
Quo Vadis GmbH webpage on the .408 Chey Tac
Jamison International LOBAEV ARMS