The 300 AAC Blackout cartridge utilizes a standard bullet diameter of 0.308 inches (7.82 mm) and a maximum case length of 1.368 inches (34.75 mm).
Its maximum overall cartridge length is standardized at 2.260 inches (57.40 mm) to ensure flawless compatibility with standard AR-15 magazines.
The lower case features a rim diameter of 0.378 inches (9.60 mm) and a maximum base diameter of 0.376 inches (9.55 mm), sharing a foundational footprint with the 5.56x45mm NATO.
Moving upward, the case features a shoulder diameter of 0.360 inches (9.14 mm) and a neck diameter of 0.334 inches (8.48 mm).
Published specifications reflect nominal design targets, maximum envelope limits, or manufacturing tolerances defined by SAAMI.
Reviewing these core geometrical figures is vital for evaluating case capacity, chamber clearance, and safe subsonic or supersonic performance.
300 AAC Blackout Dimensions
| Dimension | Inches | Millimeters | Specification Type | Source | Notes |
| Bullet Diameter | 0.308 in | 7.82 mm | Nominal | SAAMI | Standard .30 caliber projectile standard |
| Case Length | 1.368 in | 34.75 mm | Maximum | SAAMI | Maximum allowable length from case head to mouth |
| Overall Cartridge Length | 2.260 in | 57.40 mm | Maximum (COAL) | SAAMI | Designed to fit standard AR-15 magazine wells |
| Rim Diameter | 0.378 in | 9.60 mm | Maximum | SAAMI | Shares bolt-face compatibility with 5.56 NATO |
| Base Diameter | 0.376 in | 9.55 mm | Maximum | SAAMI | Body diameter just forward of the extractor groove |
| Shoulder Diameter | 0.360 in | 9.14 mm | Nominal / Max | SAAMI | Measured at the junction of the shoulder and body |
| Neck Diameter | 0.334 in | 8.48 mm | Maximum | SAAMI | Dimension at the case neck for loaded round clearance |
| Shoulder Angle | 17.5° | 17.5° | Nominal | SAAMI | Gentle 17.5-degree shoulder geometry |
| Case Capacity | 25.5 gr H₂O | 1.65 ml | Measured / Nominal Usable | Industry / SAAMI | Usable water capacity to the mouth |
| Maximum Pressure | 55,000 psi | 380 MPa | Maximum Average Pressure (MAP) | SAAMI | Upper pressure safety threshold |
Understanding The 300 AAC Blackout Dimensions
Analyzing the 300 AAC Blackout cartridge dimensions involves understanding how each geometric parameter supports multi-role functionality in both suppressed and unsuppressed setups. The bullet diameter measures 0.308 inches, allowing the cartridge to leverage a massive ecosystem of standard .30-caliber projectiles.The case length is capped at a maximum of 1.368 inches, derived by shortening and necking up a standard 5.56 NATO case.The rim diameter (0.378 inches) and base diameter (0.376 inches) match the 5.56 case head, allowing firearms to convert to 300 BLK by swapping only the barrel.
The shoulder diameter (0.360 inches) and shoulder angle (17.5 degrees) create a controlled headspacing surface while enabling smooth feeding from curved box magazines.The neck diameter (0.334 inches) ensures proper neck tension without excessive wall thickness issues.Finally, the overall cartridge length (COAL) of 2.260 inches ensures that even heavy, long-ogive subsonic bullets remain within standard magazine constraints.
300 AAC Blackout Dimensions In Inches And Millimeters
To assist reloaders and ballistic technicians, core 300 aac blackout dimensions are listed below in both inches and millimeters.
| Parameter | Inches (in) | Millimeters (mm) |
| Bullet Diameter | 0.308 in | 7.82 mm |
| Case Length (Max) | 1.368 in | 34.75 mm |
| Cartridge Overall Length (Max) | 2.260 in | 57.40 mm |
| Base Diameter | 0.376 in | 9.55 mm |
| Rim Diameter | 0.378 in | 9.60 mm |
| Shoulder Diameter | 0.360 in | 9.14 mm |
| Neck Diameter | 0.334 in | 8.48 mm |
300 AAC Blackout Case Dimensions
The 300 aac blackout case dimensions are engineered to fit standard intermediate rifle architecture while delivering robust powder volume for heavier projectiles. With a maximum case length of 1.368 inches and a base diameter of 0.376 inches, the case retains the exact head profile of the parent 223 Remington / 5.56x45mm.
The body features a slight taper leading into a 17.5-degree shoulder angle and a short neck designed to grip .308-inch bullets securely. SAAMI specifications define the maximum dimensional boundaries, though handloaders converting 5.56 brass must carefully monitor neck wall thickness to ensure proper chamber clearance.
300 AAC Blackout Bullet Diameter
The official 300 aac blackout bullet diameter is standardized at 0.308 inches (7.82 mm).This distinguishes it from smaller intermediate cartridges like the 5.56 NATO (.224 in).
It is important not to confuse bullet diameter with bore diameter (the distance across the raised rifling lands) or groove diameter (the inner diameter across the deepest valleys of the rifling). Utilizing a true .308-inch projectile diameter allows the cartridge to employ everything from lightweight 110-grain supersonic varmint bullets to ultra-heavy 220-grain subsonic match bullets.
300 AAC Blackout Overall Cartridge Length
The published maximum overall length (COAL) for the 300 aac blackout is 2.260 inches (57.40 mm). This dimension is critical because it matches the maximum length allowable in standard AR-15 magazine wells without causing binding or feeding failures.
While factory ammunition is engineered to stay at or slightly below this threshold, individual handloaders often adjust seating depths based on specific bullet ogive profiles and chamber throat geometry, ensuring the round still functions smoothly in internal magazines.
300 AAC Blackout Case Capacity
The 300 aac blackout case capacity averages roughly 25.0 to 25.5 grains of water ($H_2O$) when measured to the mouth, depending on the specific brass manufacturer.
Because many reloaders form 300 BLK brass by cutting down and resizing 5.56x45mm military or commercial cases, internal wall and web thicknesses can vary significantly between headstamps. Nominal published capacity provides a baseline, but actual measured capacity dictates powder selection—particularly for fast-burning powders used to cycle both light supersonic and heavy subsonic loads efficiently.
300 AAC Blackout Dimensions vs Similar Cartridges
Comparing the 300 AAC Blackout with other intermediate and rifle cartridges highlights its unique compact form factor.
| Cartridge | Bullet Diameter | Case Length | Overall Length | Rim / Base Diameter | Case Capacity | Source |
| 300 AAC Blackout | 0.308 in | 1.368 in | 2.260 in | Rim: 0.378 in / Base: 0.376 in | ~25.5 gr H₂O | SAAMI |
| 5.56x45mm NATO | 0.224 in | 1.760 in | 2.260 in | Rim: 0.378 in / Base: 0.376 in | ~30.0 gr H₂O | SAAMI |
| 7.62x39mm | 0.311 in | 1.528 in | 2.200 in | Rim / Base: 0.447 in | ~35.0 gr H₂O | SAAMI |
| 308 Winchester | 0.308 in | 2.015 in | 2.810 in | Rim / Base: 0.473 in | ~56.0 gr H₂O | SAAMI |
300 AAC Blackout vs 5.56 NATO Dimensions
Both the 300 AAC Blackout and the 5.56x45mm NATO share the same maximum overall cartridge length of 2.260 inches and utilize identical bolt faces, extractor dimensions, and base diameters (0.376 in).
However, the 300 BLK features a significantly shorter case length (1.368 in vs. 1.760 in) to accommodate a much wider .308-inch bullet without exceeding magazine length limits. This shorter case reduces powder capacity compared to the 5.56 NATO, but its optimized volume yields exceptional efficiency with fast-burning powders in short-barreled rifles.
300 AAC Blackout Chamber And Cartridge Dimensions
The 300 aac blackout chamber dimensions are precisely cut to accept standard loaded ammunition while ensuring safety and accuracy. Proper headspacing relies on the 17.5-degree shoulder datum.
The chamber throat features a specific leade designed to handle both stubby supersonic projectiles and long, sleek subsonic pills without jamming them into the rifling lands prematurely. Tight manufacturing tolerances ensure minimal case expansion and clean extraction.
300 AAC Blackout Bullet Weight And Dimensions
The 300 AAC Blackout accommodates a massive span of projectile weights, most commonly ranging from 110 grains up to 220+ grains.Popular options include 110-grain, 125-grain, 150-grain supersonic loads, and heavy 208-grain to 220-grain subsonic configurations.
While projectile weight does not alter standardized case dimensions, physical bullet length and ogive shape heavily dictate seating depth and overall cartridge length requirements to ensure reliable magazine feeding.
Why 300 AAC Blackout Dimensions Matter
Exact cartographic measurements dictate every element of 300 BLK performance:
- Chamber Fit & Headspacing: Ensures correct positioning off the shoulder datum for safe ignition.
- Feeding & Magazine Compatibility:Adhering to the 2.260-inch COAL allows flawless operation in standard mil-spec AR-15 magazines.
- Pressure Regulation:Conforming to SAAMI case volumes maintains peak operating pressures at or below the 55,000 psi limit.
- Component Selection: Helps prevent dangerous mix-ups with similarly dimensioned cases and guides proper reloading practices.
Manufacturer Specifications vs Independent Measurements
Official dimensions for the 300 AAC Blackout are regulated by SAAMI standards, establishing maximum envelope limits and a Maximum Average Pressure ceiling of 55,000 psi.
While factory ammunition and commercial brass strictly adhere to these blueprints, independent measurements of converted military brass or fired cases can show minor variations due to wall thickness discrepancies and resizing die differences. Official SAAMI data remains the ultimate benchmark for cartridge geometry.
Common Questions
What are the dimensions of 300 AAC Blackout?
The 300 AAC Blackout features a bullet diameter of 0.308 inches, a maximum case length of 1.368 inches, a maximum overall length of 2.260 inches, a base diameter of 0.376 inches, and a rim diameter of 0.378 inches.
What is the 300 AAC Blackout case length?
The maximum SAAMI case length is 1.368 inches (34.75 mm).
What is the 300 AAC Blackout overall length?
The maximum overall cartridge length (COAL) is 2.260 inches (57.40 mm).
What is the 300 AAC Blackout bullet diameter?
The standardized bullet diameter is 0.308 inches (7.82 mm).
What is the 300 AAC Blackout rim diameter?
The rim diameter is 0.378 inches (9.60 mm).
What is the 300 AAC Blackout base diameter?
The maximum base diameter is 0.376 inches (9.55 mm).
What is the 300 AAC Blackout case diameter?
The base diameter measures 0.376 inches maximum.
What is the 300 AAC Blackout case capacity?
Usable case capacity averages approximately 25.5 grains of water ($H_2O$).
How does 300 AAC Blackout compare with 5.56 NATO dimensions?
Both share the same 2.260-inch overall length and 0.376-inch base diameter, but the 300 BLK has a shorter case length (1.368 in vs. 1.760 in) to accommodate a .308-inch bullet.
Is 300 AAC Blackout the same size as 7.62x39mm?
No. The 7.62x39mm has a larger base and rim diameter (0.447 inches) and a longer case, whereas the 300 BLK matches the 5.56 NATO case head.
What is the maximum overall length of 300 AAC Blackout?
The maximum SAAMI overall length is 2.260 inches.
What is the 300 AAC Blackout maximum pressure?
The SAAMI Maximum Average Pressure (MAP) limit is 55,000 psi (380 MPa).