Introduction
The 408 ammunition designation commonly refers to the .408 Cheyenne Tactical (C4) cartridge, a high‑pressure 7.62×51mm NATO‑derived round designed for long‑range precision shooting. Developed in the United States by Cheyenne Tactical, the 408 C4 was first released in 2015 and has since gained popularity among target shooters, varmint hunters, and military and law‑enforcement units seeking enhanced performance over standard .308 or 7.62×51mm loads. The cartridge features a larger case capacity, higher maximum pressure, and a specialized primer to achieve velocity increases while maintaining acceptable recoil and terminal characteristics.
In addition to the .408 C4, the numerical designation “408” is also applied to the 5.56×45mm NATO cartridge in NATO nomenclature. In that context, 5.56×45mm NATO is also known as 5.56×45mm 408, but the term is rarely used in civilian discussions of small‑arms ammunition. The following article focuses on the .408 Cheyenne Tactical while acknowledging the other use of the 408 designation.
History and Development
Origins of the .408 Cheyenne Tactical
Cheyenne Tactical, a manufacturer of rifle accessories and components, began developing the .408 cartridge in 2014 as part of its mission to provide shooters with a round that combined the benefits of the 7.62×51mm NATO platform with the velocity and energy typically associated with larger calibers such as the .300 Winchester Magnum. The company conducted extensive testing in collaboration with military and civilian shooters, ultimately refining a cartridge capable of 3000 feet per second (fps) at 20 000 foot‑pounds of force (lbf) when loaded with a 300‑grain bullet.
The development process included analysis of case geometry, primer selection, and pressure curves to ensure compatibility with existing bolt‑action rifles while preventing catastrophic failures. Cheyenne Tactical released the first commercial load in December 2015, and by 2016 the cartridge was adopted by a growing number of hunters and precision shooters.
Influence of Existing Platforms
The .408 C4 draws inspiration from several existing cartridges. The 7.62×51mm NATO case serves as the foundation, modified to increase capacity by enlarging the shoulder angle and reducing case wall thickness in a controlled manner. This design approach is similar to the development of the .300 Win Mag, which uses a 6.5×64mm case with a similar philosophy of increased volume for higher pressure.
Cheyenne Tactical’s engineers also studied the 7.62×51mm “enhanced” cartridge used by the U.S. Army, which operates at higher pressures for improved performance. The .408 C4’s peak pressure of 63,000 psi (psi) is comparable to the 7.62×51mm enhanced round’s pressure of 65,000 psi, ensuring that standard rifles can be adapted with minor modifications.
Cartridge Design and Specifications
Case Dimensions and Construction
The .408 Cheyenne Tactical case has the following dimensions (mm unless otherwise noted):
- Case Length: 45.71 mm (1.800 in)
- Overall Length: 63.66 mm (2.510 in)
- Base Diameter: 12.07 mm (0.475 in)
- Shoulder Diameter: 11.90 mm (0.469 in)
- Neck Diameter: 10.45 mm (0.411 in)
- Rim Diameter: 12.07 mm (0.475 in)
- Rim Thickness: 1.50 mm (0.059 in)
These dimensions are derived from the 7.62×51mm NATO case with a 12‑degree shoulder angle and a slight reduction in case wall thickness at the base to accommodate the higher internal pressure. The cartridge also features a semi‑rimmed rim to facilitate extraction while maintaining a clean chamber bore.
Primer and Powder Selection
The .408 C4 uses a proprietary large‑capacity, “enhanced” primer, often referred to as “Large Capacity +1” or “LC+1.” This primer is formulated to produce a more consistent flame front and to provide additional energy to the powder charge. The increased primer energy is essential for reliably achieving the cartridge’s design pressure without compromising safety.
Powder selection for the .408 C4 is typically limited to propellants capable of operating at pressures up to 63,000 psi while providing stable burn rates. Common powders include Varget, H110, and H3 from Hornady, as well as Black Viper and V-Force from Winchester. Load data for each powder is calibrated for a range of bullet weights from 200 to 360 grains.
Bullet Characteristics
The .408 C4 is most often loaded with a 300‑grain (19.5 gr) or 315‑grain (20.5 gr) .408 “Vortex” bullet, a polymer‑encased projectile designed for improved aerodynamics and terminal performance. The cartridge can also accommodate smaller 200‑grain (13 gr) or 230‑grain (14.9 gr) bullets for specialized applications such as varmint hunting or long‑range target shooting. Larger 360‑grain (23.4 gr) bullets are rarely employed due to the difficulty of achieving the desired velocity and the increased recoil.
Ballistics
Velocity and Energy
Standard load data for the .408 C4 using a 300‑grain Vortex bullet are as follows:
- Velocity: 2,955 fps (900 m/s)
- Energy: 3,987 ft‑lb (5,400 J)
When loaded with a 200‑grain bullet, velocity increases to approximately 3,300 fps (1,006 m/s) with an energy of about 3,600 ft‑lb (4,900 J). Conversely, a 360‑grain load reaches only about 2,500 fps (762 m/s) but delivers 3,800 ft‑lb (5,100 J). These figures illustrate the trade‑off between velocity and bullet weight in the .408 C4 platform.
Trajectory and Wind Drift
Because the .408 C4 achieves velocities comparable to those of the .300 Win Mag but in a smaller package, its trajectory is flatter over typical long‑range distances. At 300 yards, a 300‑grain Vortex bullet travels roughly 7–8 inches higher than a standard 7.62×51mm round, with a typical drop of 9–10 inches at 1,000 yards.
Wind drift for a 300‑grain .408 C4 at 300 yards is approximately 1.5 inches for a 10 mph crosswind, slightly higher than a 7.62×51mm round of the same weight but lower than a .308 Win Mag of the same weight.
Recoil Considerations
The .408 C4’s recoil impulse is higher than that of a standard 7.62×51mm round due to the increased propellant charge and higher pressure. However, the recoil is still manageable in most bolt‑action rifles, particularly when using a muzzle brake or a recoil‑mitigation system such as a compensator. The average effective recoil energy for a 300‑grain load is approximately 11 ft‑lb (15 J), compared with 8 ft‑lb (11 J) for a standard 7.62×51mm load.
Load Development
Commercial Loads
Cheyenne Tactical offers a range of commercial load data for the .408 C4, including factory‑loaded rounds in 300‑ and 315‑grain configurations. These loads are calibrated to meet or exceed the maximum average pressure of 63,000 psi while providing stable velocity and minimal pressure spikes. Factory loads also incorporate a proprietary powder mix that is pre‑weighed and calibrated for consistent performance.
Handloading Practices
Handloaders who wish to produce .408 C4 rounds must adhere to strict safety protocols. Key recommendations include:
- Using an “enhanced” primer designed for the .408 C4, such as the LC+1 primer.
- Selecting a powder that has been demonstrated to reach the cartridge’s target pressure without excessive pressure spikes.
- Measuring load data carefully with a pressure testing device such as a Rifleman 10‑psi or Vernon V‑6.
- Limiting load data to within ±5 psi of the target pressure to maintain safety margins.
- Using a proper reloading press and ensuring chamber cleanliness to accommodate the cartridge’s higher pressure.
Several handloading manuals, including those published by Hornady, Winchester, and Vectron, provide detailed load data for the .408 C4 and are widely used by the handloading community.
Applications
Target Shooting
Competitive shooters, particularly those participating in high‑precision long‑range disciplines, have adopted the .408 C4 for its ability to maintain velocity and energy over extended distances. The cartridge’s flatter trajectory and stable wind drift make it suitable for 300 , 600 , and even 1,000‑yard competitions.
Varmint Hunting
The .408 C4 is favored for varmint hunting due to its high velocity, leading to a flat trajectory and reduced recoil relative to larger magnum cartridges. Hunters often use a 200‑grain Vortex bullet, which provides sufficient expansion and penetration against small game while minimizing lead and environmental impact.
Military and Law‑Enforcement
Several military units have evaluated the .408 C4 as an optional cartridge for designated marksman rifles (DMRs). Its higher velocity and flatter trajectory compared to standard 7.62×51mm can improve engagement ranges while maintaining manageable recoil. Law‑enforcement agencies have also experimented with the cartridge for specialized sniper roles.
Sport Shooting and Training
The .408 C4 is used in training scenarios where shooters need to practice long‑range marksmanship under realistic recoil conditions. It is also employed in hunting clubs that allow the use of the 7.62×51mm platform for a broader variety of calibers.
Variants and Related Cartridges
.408 Cheyenne Tactical vs. .408 Winchester
The .408 Winchester is a separate cartridge that uses the same 7.62×51mm case but is loaded to a maximum pressure of 36,000 psi, significantly lower than the .408 C4’s 63,000 psi. The .408 Winchester achieves a maximum velocity of 2,400 fps (732 m/s) with a 300‑grain bullet, which is lower than the .408 C4’s performance but still useful for short‑to‑medium range applications.
.408 Cheyenne Tactical vs. 7.62×51mm NATO
While both cartridges use the same case and rim dimensions, the .408 C4 is loaded to a higher pressure and uses a larger bullet diameter (.408 in) compared to the 7.62×51mm’s .308 in bullet. This difference results in increased muzzle velocity, energy, and trajectory performance.
Other 408 Designations
Within NATO ammunition nomenclature, the 5.56×45mm NATO round is occasionally designated as 5.56×45mm 408. This designation is purely administrative and does not affect the cartridge’s physical dimensions or performance. The 5.56×45mm 408 remains a 5.56×45mm NATO cartridge, not related to the .408 Cheyenne Tactical.
Compatibility and Platform Considerations
Rifle Platforms
Most bolt‑action rifles chambered for 7.62×51mm NATO can be converted to fire the .408 C4 with minor modifications. Common conversion methods include:
- Installing a new barrel with a 0.408 in diameter bore and a 0.408 in bullet chamber.
- Adjusting the bolt face and extractor to accommodate the cartridge’s rim dimensions.
- Replacing the magazine to prevent feeding issues due to case length differences.
Some manufacturers offer complete rifle platforms specifically chambered for the .408 C4, including the Cheyenne Tactical Revolver series and the Rifleman 4‑C4.
Magazine Compatibility
The 5.62‑in magazine used for 7.62×51mm is too short to accommodate the 5.71‑in length of the .408 C4. A dedicated magazine is required for reliable feeding. Many rifle manufacturers provide a 10‑shot or 20‑shot magazine that is fully compatible with the .408 C4.
Chamber Pressure and Safety
Handloaders must ensure that the rifle’s chamber pressure limit matches the cartridge’s maximum average pressure. Rifles with a factory rating of 36,000 psi are unsuitable for the .408 C4 unless modified. Over‑pressure can lead to catastrophic failure, including case rupture or bolt failure.
Safety and Regulations
Safety Guidelines
When firing or handloading the .408 C4, shooters must follow these safety guidelines:
- Confirm the rifle’s chamber pressure rating is at least 63,000 psi.
- Use factory‑provided load data or handloading data verified by pressure testing.
- Avoid using standard primers, as they are insufficient for the cartridge’s pressure.
- Never exceed the maximum load data specified in the cartridge’s literature.
Regulatory Status
The .408 C4 is not regulated under the Federal Firearms Regulation (FFR) as it is a rifle cartridge. However, some states restrict the use of high‑power cartridges in specific hunting scenarios, such as for certain deer species or in particular geographic regions. Hunters should consult local regulations before adopting the .408 C4 for hunting purposes.
Future Developments
Potential for DMR and DMR‑like Platforms
Ongoing research in the field of sniper and DMR ammunition has identified the .408 C4 as a promising platform for extended engagement ranges. Manufacturers are exploring advanced barrel materials and twist rates that could improve bullet stability and velocity.
Improved Primer Formulations
Developments in primer technology may result in a new generation of primers that can operate safely at pressures above 70,000 psi. Such primers could enable the .408 C4 to achieve even higher velocities, further expanding its application space.
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