The 450 Bushmaster is a high impact straight-walled centerfire rifle cartridge featuring a maximum case length of 1.700 inches (43.18 mm) and a maximum overall cartridge length of 2.260 inches (57.40 mm). Based on official SAAMI standards, the rebated rim case features a 0.473 inch rim diameter, a 0.500 inch base diameter, and a maximum 0.478 inch neck diameter at the case mouth. Designed to deliver massive energy from the AR-15 platform, the cartridge headspaces directly on the case mouth and does not possess a shoulder. Published specifications represent maximum material conditions, though physical measurements may vary slightly based on specific brass manufacturing tolerances.
450 Bushmaster Case Dimensions
| Case Dimension | Inches | Millimeters | Specification Type | Source | Notes |
| Case Length | 1.700 | 43.18 | Maximum | SAAMI | Standard trim to length is 1.690 in. |
| Rim Diameter | 0.473 | 12.01 | Maximum | SAAMI | Rebated rim matches the .308 Winchester bolt face. |
| Rim Thickness | 0.054 | 1.37 | Maximum | SAAMI | Controls extractor engagement. |
| Base Diameter | 0.500 | 12.70 | Maximum | SAAMI | Measured just above the extractor groove. |
| Shoulder Diameter | N/A | N/A | N/A | SAAMI | Straight-walled case. |
| Neck Diameter | 0.478 | 12.14 | Maximum | SAAMI | Outside case mouth diameter. |
| Neck Length | N/A | N/A | N/A | SAAMI | Straight-walled case. |
| Shoulder Angle | N/A | N/A | N/A | SAAMI | Straight-walled case. |
| Overall Length | 2.260 | 57.40 | Maximum | SAAMI | Fits standard AR-15 magazines. |
| Case Capacity | ~59.5 | 3.86 cm³ | Nominal (H2O) | Industry Std. | Varies slightly by brass manufacturer. |
| Maximum Pressure | 38,500 | 265.45 MPa | Max Average | SAAMI (Piezo) | Optimized for AR-15 bolt thrust limits. |
Understanding The 450 Bushmaster Case Dimensions
To understand how the 450 Bushmaster interacts with a rifle chamber, bolt, and magazine, you must analyze its discrete geometric components. Because it is classified as a straight-walled cartridge, its geometry serves a different engineering purpose than bottleneck rifle cases.
- Case Length: Measured from the base of the rim to the case mouth. This dimension dictates the space available for powder and determines exactly where the cartridge headspaces inside the chamber.
- Rim Diameter and Thickness: The rim provides the gripping surface for the rifle extractor. The 450 Bushmaster utilizes a rebated rim, meaning the rim is significantly narrower than the main case body to fit a specific standard bolt face.
- Base Diameter: This is the width of the main cartridge body just ahead of the extractor groove. The massive 0.500 inch base gives the 450 Bushmaster its large powder capacity and heavy hitting power.
- Shoulder Diameter and Geometry: The 450 Bushmaster does not have a shoulder.
- Neck Diameter and Length: Without a shoulder step, the case maintains a very slight taper from the 0.500 inch base directly to the 0.478 inch case mouth.
- Overall Cartridge Length (OAL): The measurement from the case base to the tip of the seated bullet. This 2.260 inch maximum length dictates that the cartridge will fit perfectly inside standard AR-15 platform magazines.
- 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.
450 Bushmaster Case Dimensions In Inches And Millimeters
Official SAAMI standardization utilizes inches, but metric parameters are frequently referenced by international shooters and brass manufacturers.
| Dimension | Measurement (Inches) | Measurement (Millimeters) |
| Maximum Case Length | 1.700 in | 43.18 mm |
| Maximum Rim Diameter | 0.473 in | 12.01 mm |
| Maximum Base Diameter | 0.500 in | 12.70 mm |
| Maximum Neck Diameter | 0.478 in | 12.14 mm |
| Maximum Overall Length | 2.260 in | 57.40 mm |
450 Bushmaster Case Length
The published maximum case length for the 450 Bushmaster is 1.700 inches (43.18 mm). This specific dimension was chosen to allow the cartridge to seat long, heavy 0.452 caliber pistol bullets while remaining within the strict 2.260 inch overall length limit of the AR-15 magazine well.
Because straight-walled cases headspace directly on the case mouth rather than a shoulder, consistent case length is highly critical. If a case is trimmed too short, the firing pin may push the cartridge too far forward into the chamber, resulting in a light strike and a failure to fire. Most reloaders use a precise trim length of 1.690 inches to ensure safe headspacing and a uniform taper crimp on every round.
450 Bushmaster Base And Rim Dimensions
The 450 Bushmaster features an aggressive rebated rim design. The base diameter of the main case body measures a massive 0.500 inches, but the rim diameter is heavily rebated down to 0.473 inches.
This 0.473 inch rim is a foundational industry standard, sharing the exact same bolt face dimensions as the .308 Winchester. While the 450 Bushmaster fits inside an AR-15, it cannot use a standard 5.56 NATO bolt. It requires an AR-15 bolt that has been opened up to accept the larger 0.473 inch rim. The rebated design allows the cartridge to pack magnum powder capacities into a fat 0.500 inch body while keeping the rear of the case small enough to function in AR-15 bolt carrier groups.
450 Bushmaster Shoulder And Neck Dimensions
Unlike traditional bottleneck rifle cartridges, the 450 Bushmaster is classified as a straight-walled cartridge. It possesses no shoulder diameter, no shoulder angle, and no distinct neck length.
The brass simply extends forward from the 0.500 inch base to a maximum neck diameter of 0.478 inches at the case mouth. This slight body taper of 0.022 inches from the base to the mouth exists to prevent the brass from swelling and sticking to the chamber walls during extraction. The neck holds a 0.452 inch diameter bullet, a diameter commonly shared with the 45 Colt and 454 Casull.
450 Bushmaster Case Capacity
Case capacity heavily influences powder selection, velocity potential, and safe operating pressures. The nominal water capacity of the 450 Bushmaster is approximately 59.5 grains of H2O.
However, this internal volume fluctuates based on which manufacturer produces the brass. Thicker brass webbing near the case head will reduce internal volume. A reduction in case capacity causes standard powder charges to produce higher pressures. The 450 Bushmaster operates at a relatively low maximum pressure of 38,500 psi to prevent the large 0.500 inch case head from generating too much bolt thrust and shearing the locking lugs off an AR-15 bolt.
450 Bushmaster Case Dimensions vs 458 SOCOM
The 450 Bushmaster and the 458 SOCOM are intense rivals in the big bore AR-15 market, but their case geometries are completely different.
| Dimension | 450 Bushmaster | 458 SOCOM | Source |
| Case Length | 1.700 in | 1.575 in | SAAMI / Industry |
| Rim Diameter | 0.473 in (Rebated) | 0.473 in (Rebated) | SAAMI / Industry |
| Base Diameter | 0.500 in | 0.538 in | SAAMI / Industry |
| Bullet Diameter | 0.452 in | 0.458 in | SAAMI / Industry |
| Overall Length | 2.260 in | 2.260 in | SAAMI / Industry |
| Case Type | Straight-Walled | Bottleneck | Visual Spec |
While both cartridges share the same 2.260 inch maximum overall length and 0.473 inch rebated rim, everything else differs. The 450 Bushmaster is a straight-walled cartridge firing a 0.452 inch pistol bullet. The 458 SOCOM is a bottleneck cartridge firing a larger 0.458 inch rifle bullet. Because the 458 SOCOM has a shoulder, its case length is much shorter (1.575 inches) and its base is significantly wider (0.538 inches).
450 Bushmaster Case Dimensions vs 50 Beowulf
The 50 Beowulf is another heavy hitting AR-15 cartridge designed for extreme close range stopping power.
| Dimension | 450 Bushmaster | 50 Beowulf | Source |
| Case Length | 1.700 in | 1.650 in | SAAMI / Alexander Arms |
| Rim Diameter | 0.473 in | 0.447 in | SAAMI / Alexander Arms |
| Base Diameter | 0.500 in | 0.535 in | SAAMI / Alexander Arms |
| Bullet Diameter | 0.452 in | 0.500 in | SAAMI / Alexander Arms |
| Overall Length | 2.260 in | 2.250 in | SAAMI / Alexander Arms |
Both are straight-walled, rebated rim cartridges. However, the 50 Beowulf fires a massive half inch (0.500 caliber) bullet. To accommodate this, the 50 Beowulf uses a much wider 0.535 inch base diameter and a smaller 0.447 inch rim (matching the 7.62x39mm bolt face). The 450 Bushmaster uses a narrower 0.500 inch base and a larger 0.473 inch rim.
450 Bushmaster vs 400 Legend Case Dimensions
With the rise of straight-walled hunting regulations in the midwest, the 400 Legend was introduced as a modern alternative to the older 450 Bushmaster.
The 450 Bushmaster is significantly wider and more powerful. It uses a 0.500 inch base, a 0.473 inch rim, and a 1.700 inch case length. The newer 400 Legend is slimmer, utilizing a 0.440 inch base, a 0.422 inch rim (6.8 SPC bolt face), and a 1.650 inch case length. Because the 400 Legend is narrower, it generates less recoil and allows more rounds to be stacked inside a standard box magazine.
450 Bushmaster Chamber And Case Dimensions
A rifle chamber must be fractionally larger than the cartridge it accepts. The relationship between 450 Bushmaster case dimensions and chamber dimensions centers entirely on the case mouth.
Because there is no shoulder, headspace for the 450 Bushmaster is measured from the bolt face to the lip of the chamber throat. The brass mouth physically impacts this internal chamber lip to stop the cartridge from sliding forward. Unlike revolver cartridges that use a heavy roll crimp, the 450 Bushmaster must use a taper crimp. A roll crimp would fold the brass inward, destroying the square edge needed to headspace on the chamber lip and causing dangerous misfires.
450 Bushmaster Case Forming And Resizing
The 450 Bushmaster traces its lineage directly back to the .284 Winchester cartridge. Handloaders can technically form 450 Bushmaster brass from .284 Winchester cases.
This process involves cutting the longer .284 Winchester case down to 1.700 inches and running it through an expander die to straighten out the walls and remove the shoulder. Because the .284 Winchester shares the exact same 0.473 inch rebated rim and 0.500 inch base diameter, the conversion creates a dimensionally perfect 450 Bushmaster case.
450 Bushmaster Manufacturer Specifications vs Actual Measurements
There is a documented difference between absolute 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 extract cleanly from dirty or tightly machined chambers. A fired 450 Bushmaster case expands to the exact dimensions of the specific rifle chamber it was fired in. When a handloader runs this fired brass through a carbide sizing die, the machine compresses the base and body back down to factory nominal tolerances.
Common Questions
What are the 450 Bushmaster case dimensions?
The key maximum case dimensions for the 450 Bushmaster include a 1.700 inch case length, a 0.473 inch rebated rim diameter, a 0.500 inch base diameter, and a 0.478 inch neck diameter at the case mouth.
What is the 450 Bushmaster case length?
The maximum SAAMI case length for the 450 Bushmaster is 1.700 inches (43.18 mm). The standard trim to length for reloading is 1.690 inches.
What is the 450 Bushmaster rim diameter?
The 450 Bushmaster features a rebated rim with a maximum diameter of 0.473 inches (12.01 mm), which matches a standard .308 Winchester style bolt face.
What is the 450 Bushmaster base diameter?
The base diameter of the 450 Bushmaster, measured just above the extractor groove, is 0.500 inches (12.70 mm).
What is the 450 Bushmaster shoulder diameter?
The 450 Bushmaster is a straight-walled cartridge and does not possess a shoulder.
What is the 450 Bushmaster neck diameter?
The maximum outside neck diameter at the case mouth for the 450 Bushmaster is 0.478 inches (12.14 mm).
What is the 450 Bushmaster case capacity?
The nominal case capacity of the 450 Bushmaster is approximately 59.5 grains of water (H2O), or 3.86 cubic centimeters.
What is the 450 Bushmaster overall length?
The maximum overall cartridge length (OAL) for the 450 Bushmaster is 2.260 inches (57.40 mm) under SAAMI specifications.
How does 450 Bushmaster compare with 458 SOCOM case dimensions?
While both fit in an AR-15 and use a 0.473 inch rim, they are fundamentally different. The 450 Bushmaster is a straight-walled case measuring 1.700 inches long with a 0.500 inch base. The 458 SOCOM is a bottleneck cartridge measuring 1.575 inches long with a much wider 0.538 inch base.
Are 450 Bushmaster and 400 Legend case dimensions the same?
No. The 450 Bushmaster is significantly wider at the base (0.500 inches versus 0.440 inches) and utilizes a larger rim diameter (0.473 inches versus 0.422 inches). They are not interchangeable and require completely different bolt faces.
What is the 450 Bushmaster maximum pressure?
The SAAMI maximum average pressure (MAP) for the 450 Bushmaster is 38,500 psi (piezo method). This lower pressure limit prevents the wide cartridge base from exerting excessive bolt thrust on the AR-15 locking lugs.