When a bullet is fired underwater, it will travel much shorter distances than when fired in air. The dense water medium causes a bullet to quickly lose velocity due to drag forces. However, a bullet’s maximum travel distance depends on multiple factors, including the bullet’s shape, mass, initial velocity, and the water conditions.
Quick Summary
In general, a typical bullet fired from a handgun can travel about 8-12 inches (20-30 cm) underwater before coming to a stop. High velocity rifle bullets travel farther, perhaps up to 3-4 feet (around 1 meter). Very low drag rounds like solids or slugs achieve the greatest distances, but still no more than 5-8 feet (1.5-2.5 m) in most cases. The water depth, temperature, salinity, and other factors also affect the bullet’s trajectory.
How Drag Forces Limit Underwater Bullet Travel
When any object moves through a fluid like water, it experiences drag forces that oppose its motion. The faster the speed, the greater the drag. There are two main types of drag force:
- Form drag – Due to the frontal area shape of the object pushing through the water
- Skin friction drag – Due to the viscous friction along the object’s wetted surface area
Both types of drag on a bullet get progressively stronger the farther it travels. The denser water medium causes drag forces to increase much more rapidly compared to air. At some point, the bullet slows to a stop as the drag equals the forward momentum.
Form Drag Effects
Form drag on a bullet stems from its elongated, non-streamlined profile. The blunt nose experiences high pressure drag as it pushes water aside. Turbulence forms behind the nose and along the sides, creating low pressure that resists motion. Bullets are designed for stability in air, not water. Deformation from impact can also increase form drag if the bullet tumbles or yaws sideways.
Skin Friction Drag Effects
Skin friction results from the bullet’s frontal area and surface roughness rubbing through the viscous water. The wetted surface area in contact with the water is increased compared to air. Higher velocity increases skin friction proportionally. The bullet’s rotation as it travels also pumps more water across its surface, compounding this effect.
Viscous Nature of Water
Water has a viscosity nearly 1,000 times higher than air. Viscosity measures a fluid’s resistance to deformation or flow. Low viscosity allows objects to move through with minimal friction. High viscosity causes more drag on the object. This property greatly limits a bullet’s range underwater.
Factors Affecting Underwater Bullet Travel Distance
While underwater bullets travel very short distances overall, their maximum range depends on several factors:
Bullet Mass and Shape
- Heavier bullets are less affected by drag
- Elongated bullet shapes have high form drag
- Rounder nose profiles like hollowpoints reduce drag
- Solid, monolithic shapes have the lowest drag
Muzzle Velocity
- Higher muzzle velocity equals greater max distance
- Typical handgun velocity: 1,000 – 1,400 fps
- High velocity rifles: over 3,000 fps
Water Conditions
- Deeper water increases travel distance
- Higher temperature lowers water density and drag
- Greater salinity also increases water density
- Higher viscosity equals greater drag on the bullet
Bullet Integrity
- Bullet metal and construction affects deformation
- Jacketed rounds hold together better than lead
- Fragmentation increases drag and shortens range
Angle of Entry
- Steeper angle preserves more velocity
- Shallow angle bleeds off energy quickly
Typical Handgun Bullet Performance Underwater
For common pistol rounds fired underwater, the bullet usually travels no more than 1 foot (30 cm) before coming to rest. Several factors contribute to such limited range:
- Relatively low velocities, less than 1,400 fps
- Moderate bullet mass, 115 to 147 grains
- Higher drag shape with exposed lead tip
- High deformation and fragmentation
9mm Luger FMJ ammunition from a typical 4″ barrel handgun achieves the following average results when fired into water:
| Bullet Type | Velocity (fps) | Travel Distance |
|---|---|---|
| 9mm 115gr FMJ | 1100 | 8-10 inches |
| 9mm 124gr FMJ | 1050 | 10-12 inches |
| 9mm 147gr FMJ | 980 | 12 inches |
.40 S&W and .45 ACP FMJ rounds perform similarly, with 155gr and 230gr bullets traveling around 8-12 inches on average.
Bullet Spin and Yawing
The rapid 1:7 to 1:10 twist rate of many pistol barrels causes the bullet to spin at thousands of RPM as it enters the water. This destabilizes the bullet and leads to yawing and tumbling. The increased frontal area exponentially increases form drag, quickly bleeding velocity.
Fragmentation Effects
The temporary cavitation caused by impact with the water’s surface can deform, fracture, or even fragment the bullet. Partial fragmentation greatly increases surface area and skin friction drag. The bullet pieces also disperse and decelerate rapidly.
Typical Rifle Bullet Performance Underwater
High velocity rifle bullets, traveling over 2,000 fps, achieve moderately increased range underwater compared to pistols. However, performance is still severely limited by drag forces. Total travel distances are less than 5 feet (1.5 meters) for most rounds.
Key factors for increased rifle bullet range include:
- Greater mass for momentum
- Much higher initial velocity
- Low-drag nose profiles
5.56x45mm FMJ rifle ammunition from a 20″ barrel achieves approximately:
| Bullet Type | Velocity (fps) | Travel Distance |
|---|---|---|
| 55gr FMJ | 3100 | 36-48 inches |
| 62gr FMJ | 2950 | 48-60 inches |
The longer 24″ barrel of a 7.62x51mm (.308) rifle provides greater velocity and energy for increased bullet travel underwater:
| Bullet Type | Velocity (fps) | Travel Distance |
|---|---|---|
| 150gr FMJ | 2850 | 48-60 inches |
| 168gr FMJ | 2700 | 60-72 inches |
Longer Spin Stabilization
The slower 1:8 to 1:12 twist rate of rifle barrels delays destabilization effects somewhat. This maintains a steadier trajectory for a longer duration before yawing occurs.
Bullet Construction
Jacketed rifle bullets hold together better than exposed lead handgun rounds. However, deformation and fracturing still occur, limiting range. Solid copper or turned metal rounds have the best performance for maximum bullet integrity.
Specialized Subsonic Ammunition
Specially designed subsonic ammo using heavy, streamlined bullets can achieve increased underwater travel compared to normal rounds. These specialty loads are purpose-built for superior external and terminal ballistics in water.
Typical characteristics include:
- Heavy rounded nose or flat point bullet
- All copper or turned solid metal construction
- Minimal velocity of 1,000 – 1,100 fps
- Waterproof sealed case
Underwater ranges achievable with such optimized ammunition can exceed 10 feet (3 meters) in some cases.
| Bullet Type | Velocity (fps) | Travel Distance |
|---|---|---|
| 220gr RNFP | 1050 | 36-48 inches |
| 350gr Solids | 975 | 48-60 inches |
These represent the maximum travel distances possible for non-deforming projectiles through water.
Key Factors Limiting Underwater Bullet Travel
In summary, the key factors limiting underwater bullet travel include:
- High drag forces
- Low velocity
- Tumbling and yawing
- Deformation and fragmentation
- Viscosity effects
No conventional bullet overcomes these effects enough to travel more than 5-8 feet underwater. Velocities quickly drop below 150 fps where bullets have little penetrating power. Specialized ammo design is needed to achieve marginally improved range underwater.
Conclusion
In conclusion, a typical bullet fired underwater from a handgun or rifle will travel only a very short distance. While a variety of factors affect underwater trajectory, the limiting element is the high density and viscosity of water creating tremendous drag forces. No normal bullet travels more than 1-5 feet maximum before coming to rest. Only specially designed subsonic ammo with optimized heavy projectiles can extend an underwater bullet’s range slightly beyond this limit. But the performance is still severely curtailed compared to firing through air.