The .277 Fury, officially standardized by SAAMI as the 277 SIG FURY and adopted by the U.S. military as the 6.8x51mm, is a high pressure short action centerfire rifle cartridge featuring a maximum case length of 2.015 inches (51.18 mm) and an overall cartridge length of 2.825 inches (71.76 mm).Based on official SAAMI standards, the case features a 0.4720 inch rim diameter, a 0.4703 inch base diameter, a 0.4611 inch shoulder diameter, and a maximum neck diameter of 0.3100 inches.Unlike conventional ammunition, full power .277 Fury cartridges utilize a three piece hybrid case consisting of a brass body and a stainless steel case head to withstand extreme chamber pressures up to 80,000 psi. Published specifications can vary slightly depending on whether they represent maximum material conditions, nominal dimensions, or specific manufacturer tolerances across different construction types.
.277 Fury Case Dimensions
| Case Dimension | Inches | Millimeters | Specification Type | Source | Notes |
| Case Length | 2.015 | 51.18 | Maximum | SAAMI | Standard trim to length is 2.005 in. |
| Rim Diameter | 0.4720 | 11.99 | Maximum | SAAMI | Standard short action bolt face. |
| Rim Thickness | 0.0540 | 1.37 | Maximum | SAAMI | Controls extractor engagement. |
| Base Diameter | 0.4703 | 11.95 | Maximum | SAAMI | Measured just above the extractor groove. |
| Shoulder Diameter | 0.4611 | 11.71 | Maximum | SAAMI | Body to shoulder intersection. |
| Neck Diameter | 0.3100 | 7.87 | Maximum | SAAMI | Outside case neck diameter. |
| Overall Length | 2.825 | 71.76 | Maximum | SAAMI | Fits standard short action magazines. |
| Case Capacity | ~57.0 | 3.69 cm³ | Nominal (H2O) | Industry Std. | Varies between brass and hybrid cases. |
| Maximum Pressure | 80,000 | 551.58 MPa | Max Average | SAAMI (Piezo) | Achieved using a hybrid case head. |
Understanding The .277 Fury Case Dimensions
To understand how the .277 Fury interacts with a rifle chamber, bolt, and magazine, you must analyze its discrete geometric components. Each dimension serves a specific engineering purpose to balance powder capacity with the extreme pressures required to meet military performance standards.
- Case Length: Measured from the base of the rim to the case mouth, case length determines how far the brass extends into the chamber before contacting the end of the neck clearance.
- Rim Diameter and Thickness: The rim provides the gripping surface for the rifle extractor. The diameter ensures the cartridge centers on a standard short action bolt face, while the thickness affects how securely the extractor engages the hybrid steel base.
- Base Diameter: This is the widest part of the main cartridge body, situated just ahead of the extractor groove. It governs how the cartridge seats into the rear of the chamber and stacks within a magazine.
- Shoulder Diameter and Geometry: The shoulder acts as the physical stop that prevents the cartridge from pushing too far into the barrel. Its diameter dictates chamber fit, headspacing, and powder column efficiency.
- Neck Diameter: The neck holds the bullet. The outside diameter must clear the chamber walls to allow the brass to expand and release the projectile safely upon firing.
- Overall Cartridge Length (OAL): The measurement from the case base to the tip of the seated bullet. It dictates magazine fit and whether the bullet will prematurely engage the rifling lands.
- Case Capacity: The internal volume of the case, generally expressed in grains of water (gr H2O). This dictates the maximum powder charge the cartridge can safely hold to generate its high operating pressure.
.277 Fury Case Dimensions In Inches And Millimeters
Official SAAMI standardization utilizes inches, but metric parameters are frequently referenced by international precision shooters and military bodies.
| Dimension | Measurement (Inches) | Measurement (Millimeters) |
| Maximum Case Length | 2.015 in | 51.18 mm |
| Maximum Rim Diameter | 0.4720 in | 11.99 mm |
| Maximum Base Diameter | 0.4703 in | 11.95 mm |
| Maximum Shoulder Diameter | 0.4611 in | 11.71 mm |
| Maximum Neck Diameter | 0.3100 in | 7.87 mm |
| Maximum Overall Length | 2.825 in | 71.76 mm |
.277 Fury Case Length
The published maximum case length for the .277 Fury is 2.015 inches (51.18 mm). This perfectly matches the case length of its parent cartridge, the .308 Winchester.
Operating precisely at this maximum can cause safety issues if the case stretches during firing and pinches inside the chamber throat, resulting in dangerous pressure spikes. Therefore, handloaders universally utilize a trim to length of 2.005 inches. This nominal case length provides a 0.010 inch buffer to ensure consistent chamber fit and safe bullet release. The hybrid steel base of the military grade ammunition mitigates some stretching at the case head, but the brass body and neck will still flow forward over multiple firings.
.277 Fury Base And Rim Dimensions
The .277 Fury features a rimless, bottleneck design. Its base diameter measures 0.4703 inches, while the rim diameter is slightly wider at 0.4720 inches.
This 0.4720 inch rim diameter is a foundational standard shared by the .308 Winchester family. It dictates that the cartridge fits perfectly on a standard short action bolt face. To handle the incredible 80,000 psi chamber pressure, the military and full power commercial variants utilize a stainless steel case head combined with an aluminum locking washer that connects to the brass body. This steel base prevents the 0.4703 inch case head from yielding and destroying the rifle at pressures that would turn a traditional solid brass case into shrapnel.
.277 Fury Shoulder And Neck Dimensions
Above the straight taper of the body, the case steps down to grip a .277 caliber (7mm class) bullet. The shoulder diameter at the intersection of the case body is 0.4611 inches.
The neck diameter reaches a maximum allowable SAAMI specification of 0.3100 inches. To safely release a 0.2780 inch bullet, the chamber neck must be slightly wider than the cartridge neck. A loaded cartridge typically measures slightly below the maximum neck diameter depending on the brass wall thickness. The shoulder is pushed slightly further forward and features less taper than a standard .308 Winchester, which helps maximize powder capacity within the strict 2.015 inch case length constraint.
.277 Fury Case Capacity
Case capacity heavily influences internal ballistics, powder selection, and pressure generation. The nominal, industry accepted capacity for the unfired .277 Fury hybrid case is approximately 57.0 grains of water (H2O), or roughly 3.69 cubic centimeters.
This capacity makes the .277 Fury highly efficient. However, case capacity is not a static specification. It fluctuates wildly between the three piece hybrid cases and the traditional solid brass cases sold for reduced pressure practice ammunition. Reloaders must carefully segregate their brass types, as the internal volume and pressure handling characteristics of a solid brass .277 Fury case are vastly different from the stainless steel hybrid cases.
.277 Fury Case Dimensions vs .308 Winchester
The .277 Fury is a direct evolutionary descendant of the .308 Winchester, modified to accept higher pressures and a more aerodynamic projectile.
| Dimension | .277 Fury | .308 Winchester | Source |
| Case Length | 2.015 in | 2.015 in | SAAMI |
| Rim Diameter | 0.4720 in | 0.4730 in | SAAMI |
| Base Diameter | 0.4703 in | 0.4703 in | SAAMI |
| Shoulder Diameter | 0.4611 in | 0.4540 in | SAAMI |
| Neck Diameter | 0.3100 in | 0.3435 in | SAAMI |
| Overall Length | 2.825 in | 2.810 in | SAAMI |
| Case Capacity | ~57.0 gr H2O | ~56.0 gr H2O | Standard Data |
The cartridges share identical 2.015 inch case lengths and effectively identical base and rim diameters. The .277 Fury gains a slight capacity advantage by utilizing a wider 0.4611 inch shoulder diameter, meaning the case body has less taper than the .308 Winchester. The critical difference is the pressure limit. The .308 Winchester maxes out at 62,000 psi, while the hybrid .277 Fury is rated for 80,000 psi.
.277 Fury Case Dimensions vs 6.8 SPC
Despite both firing a .277 caliber projectile, the .277 Fury and the older 6.8 SPC are completely different cartridges designed for different rifle platforms.
| Dimension | .277 Fury | 6.8 SPC | Source |
| Case Length | 2.015 in | 1.687 in | SAAMI |
| Base Diameter | 0.4703 in | 0.4220 in | SAAMI |
| Rim Diameter | 0.4720 in | 0.4220 in | SAAMI |
| Overall Length | 2.825 in | 2.260 in | SAAMI |
| Case Capacity | ~57.0 gr H2O | ~36.9 gr H2O | Standard Data |
The 6.8 SPC was designed to fit inside the standard AR-15 magazine well, restricting it to a 2.260 inch overall length and a smaller 0.422 inch base diameter. The .277 Fury is a full sized short action cartridge designed for the AR-10 or SIG MCX Spear platform. It holds nearly 20 grains more powder and operates at significantly higher pressures, delivering vastly superior kinetic energy and effective range.
.277 Fury Chamber And Case Dimensions
A rifle chamber must be fractionally larger than the cartridge it accepts. The relationship between .277 Fury case dimensions and chamber dimensions centers heavily on headspacing and pressure containment.
Headspace for the .277 Fury is measured from the bolt face to a specific datum line on the case shoulder. Because the cartridge operates at 80,000 psi, chamber dimensions and metallurgy are strictly controlled. The hybrid steel case head prevents the base of the cartridge from expanding dangerously into the unsupported region of the breech. Proper cartridge dimensions ensure safe alignment, efficient extraction, and reliable bullet entry into the fast rifling twist required to stabilize heavy 150 grain projectiles.
.277 Fury Case Forming And Resizing
Because the .277 Fury shares the same base dimensions as the .308 Winchester, a handloader could theoretically form a .277 Fury case from standard .308 Winchester brass by pushing the shoulder forward and necking it down.
However, doing so is incredibly dangerous. A standard brass .308 Winchester case converted to .277 Fury dimensions will not possess the stainless steel hybrid case head. If a handloader attempts to load that standard brass case to the 80,000 psi specifications of the .277 Fury, the solid brass case head will catastrophically fail, rupturing and potentially destroying the firearm. Handloaders must strictly use dedicated .277 Fury hybrid cases if they intend to duplicate military velocities, or stick to severely reduced load data when using standard brass cases.
.277 Fury Manufacturer Specifications vs Actual Measurements
There is a documented difference between absolute SAAMI standards and the dimensions of a physical cartridge sitting on a reloading bench.
SAAMI lists maximum material conditions. Ammunition manufacturers intentionally produce brass slightly smaller than these maximums to guarantee their cartridges will chamber in any rifle, regardless of how tightly the manufacturer cut the chamber. A fired .277 Fury case expands to the exact dimensions of the specific rifle chamber it was fired in. When a handloader runs this fired brass through a full length sizing die, the machine compresses the base, shoulder, and neck back down to factory nominal tolerances.
Common Questions
What are the .277 Fury case dimensions?
The key maximum case dimensions for the .277 Fury include a 2.015 inch case length, a 0.4720 inch rim diameter, a 0.4703 inch base diameter, a 0.4611 inch shoulder diameter, and a 0.3100 inch neck diameter.
What is the .277 Fury case length?
The maximum SAAMI case length for the .277 Fury is 2.015 inches (51.18 mm). The standard trim to length for reloading is 2.005 inches.
What is the .277 Fury rim diameter?
The .277 Fury rim diameter is 0.4720 inches (11.99 mm max), which fits standard short action bolt faces common to the .308 Winchester.
What is the .277 Fury base diameter?
The base diameter of the .277 Fury, measured just above the extractor groove, is 0.4703 inches (11.95 mm max).
What is the .277 Fury shoulder diameter?
The maximum shoulder diameter of the .277 Fury is 0.4611 inches (11.71 mm).
What is the .277 Fury neck diameter?
The maximum outside neck diameter of the .277 Fury is 0.3100 inches (7.87 mm).
What is the .277 Fury case capacity?
The nominal case capacity of the .277 Fury hybrid case is approximately 57.0 grains of water (H2O), or 3.69 cubic centimeters. Solid brass practice cases will have slightly different internal capacities.
What is the .277 Fury overall length?
The maximum overall cartridge length for the .277 Fury is 2.825 inches (71.76 mm) under SAAMI specifications, designed to fit standard short action magazines.
How does .277 Fury compare with .308 Winchester case dimensions?
The .277 Fury utilizes the exact same 2.015 inch case length and 0.4720 inch rim diameter as the .308 Winchester. However, it features less body taper with a wider 0.4611 inch shoulder diameter, and a smaller neck to hold a .277 caliber bullet instead of a .308 caliber bullet.
How does .277 Fury compare with 6.8 SPC case dimensions?
The .277 Fury is significantly larger. The .277 Fury has a 2.015 inch case length and a 0.4703 inch base. The 6.8 SPC is restricted to AR-15 dimensions, utilizing a shorter 1.687 inch case length and a narrower 0.4220 inch base.
What is the .277 Fury maximum pressure?
The SAAMI maximum average pressure for the .277 Fury is an unprecedented 80,000 psi (551.58 MPa). This is achieved using a patented three piece hybrid case with a stainless steel base, as traditional solid brass cases cannot withstand pressures of this magnitude.