The .50 Browning Machine Gun (.50 BMG or 12.7x99mm NATO) utilizes one of the most massive projectiles available for shoulder fired rifles and heavy machine guns. The standard maximum bullet diameter is strictly defined at 0.510 inches (12.95 mm). Unlike cartridge casing dimensions which are standardized to fit specific chamber tolerances, bullet dimensions such as overall length and bearing surface vary drastically depending on the weight and intended application of the projectile. Common bullet weights range from the 647 grain military M33 Ball to massive 750 grain and 800 grain solid brass match bullets. These extreme weights require exceptionally long projectiles, often measuring between 2.28 inches and 2.70 inches in length, to achieve their legendary long range ballistic coefficients.
.50 BMG Bullet Dimensions
| Dimension | Specification | Source | Notes |
| Bullet Diameter | 0.510 in (12.95 mm) | SAAMI | Standard maximum diameter for the projectile. |
| Bullet Length (M33 Ball) | ~ 2.280 in (57.91 mm) | Military Standard | Approximate length for standard 660 grain FMJ projectiles. |
| Bullet Length (Match) | 2.500 to 2.700 in | Industry Standard | Typical length for heavy 750 grain or solid target bullets. |
| Boat Tail Angle | 9 degrees | Military Standard | Typical base angle for standard military ball ammunition. |
| Sectional Density (660 gr) | 0.362 | Industry Standard | Determines penetration capabilities of military ball. |
| Sectional Density (750 gr) | 0.412 | Industry Standard | Exceptional stability for precision long range flight. |
| Bearing Surface | Varies by design | Industry Standard | The flat portion of the bullet that engages the barrel rifling. |
Understanding The .50 BMG Bullet Dimensions
- Bullet Diameter: The measurement across the widest point of the projectile. For the .50 BMG, this is specified as 0.510 inches. This massive dimension ensures the heavy projectile seals properly within the barrel grooves to trap expanding gases and generate extreme muzzle energy.
- Bullet Length: Because the diameter is restricted to 0.510 inches, the only way to increase the weight of a .50 BMG bullet is to make it longer. Standard 660 grain bullets measure roughly 2.28 inches long, while extreme 800 grain target bullets can approach 2.80 inches.
- Boat Tail Angle: The taper at the rear of the bullet base. A 9 degree boat tail is common on military projectiles to reduce aerodynamic drag at transonic and subsonic speeds, allowing the massive bullet to retain energy over extreme distances.
- Sectional Density: A ratio of the bullet weight to its diameter. The massive sectional density of the .50 BMG (0.412 for a 750 grain bullet) is the primary reason the cartridge possesses such devastating armor penetrating and barrier blind capabilities.
- Bearing Surface: The cylindrical section of the bullet that physically contacts the rifling. Longer bearing surfaces provide better stabilization but create more friction, which can increase chamber pressures.
.50 BMG Bullet Dimensions In Inches And Millimeters
For ballisticians, reloaders, and custom projectile turners, below are the primary .50 BMG bullet measurements converted accurately between imperial and metric systems.
| Dimension | Inches | Millimeters |
| Bullet Diameter | 0.510 in | 12.95 mm |
| M33 Ball Length | 2.280 in | 57.91 mm |
| Match Bullet Length | 2.650 in | 67.31 mm |
| A-MAX Bullet Length | 2.700 in | 68.58 mm |
.50 BMG Bullet Weight And Length Variations
The .50 BMG is heavily standardized around specific military bullet designs, but the commercial market has introduced massive variations in projectile length.
- 647 to 660 grain (M33 Ball): The traditional military standard. These bullets consist of a mild steel core wrapped in a gilding metal jacket. They are relatively short for the caliber (roughly 2.28 inches) and fit easily into linked machine gun belts.
- 750 grain (Hornady A-MAX): A commercially produced match bullet featuring an aluminum tip. Because it utilizes a lighter aluminum tip and a heavy lead core, it must be exceptionally long (roughly 2.70 inches) to reach 750 grains, providing an incredible ballistic coefficient of 1.050.
- 762 to 800 grain (Solid Brass): Extreme long range shooters often use bullets turned from solid brass or copper on CNC lathes. Because copper and brass are less dense than lead, these solid bullets must be manufactured even longer than traditional lead core bullets to achieve the same weight.
.50 BMG Bore And Groove Dimensions
To understand how the 0.510 inch bullet functions, it must be compared to the internal dimensions of the barrel it is fired through.
The standard .50 BMG barrel features a groove diameter of 0.510 inches and a bore diameter (measured across the lands) of 0.500 inches. When the cartridge is fired, the 0.510 inch bullet is forced into the 0.500 inch bore. The copper jacket of the bullet is physically displaced and squeezed by the lands, engraving the rifling into the side of the bullet. This tight dimensional fit creates a perfect gas seal and imparts the aggressive spin required to stabilize a bullet that is more than two and a half inches long. Typical twist rates for a .50 BMG barrel are 1 in 15 inches.
.50 BMG Bullet vs Other .50 Caliber Bullets
The term “50 caliber” is used loosely in the firearms industry and creates significant dimensional confusion. The .50 BMG bullet is unique and generally not interchangeable with other .50 caliber firearms.
- .50 BMG: Utilizes a true 0.510 inch bullet diameter designed for extreme rifle velocities.
- .50 Beowulf: Utilizes a 0.500 inch bullet diameter designed for the AR-15 platform.
- .500 S&W Magnum: Utilizes a 0.500 inch bullet diameter designed for heavy revolvers.
- .50 Action Express: Utilizes a 0.500 inch bullet diameter designed for the Desert Eagle pistol.
You cannot use 0.500 inch pistol bullets in a .50 BMG rifle. The undersized 0.500 inch bullet will rattle down the 0.510 inch grooves of the .50 BMG barrel, allowing high pressure gases to escape past the projectile. This destroys accuracy, severely fouls the barrel, and creates dangerous pressure variations.
Common Questions
What is the diameter of a .50 BMG bullet?
The standardized maximum bullet diameter is strictly 0.510 inches (12.95 mm).
How long is a .50 BMG bullet?
Bullet length varies by weight and design. Standard military M33 ball bullets are approximately 2.28 inches long, while heavy 750 grain match bullets can measure 2.70 inches long.
Can I use .500 S&W bullets in a .50 BMG?
No. The .500 S&W uses a 0.500 inch bullet, which is dangerously undersized for the 0.510 inch groove diameter of a .50 BMG rifle barrel.
What is the core of a .50 BMG bullet made of?
Commercial target bullets typically feature lead cores with copper jackets or are machined from solid brass or copper. Military ball ammunition often utilizes mild steel cores to maintain a specific weight and length profile while reducing lead usage.
What is the sectional density of a .50 BMG bullet?
A standard 660 grain bullet has a sectional density of 0.362, and a heavy 750 grain target bullet has a massive sectional density of 0.412.