Myth or Fact: Do Fragments from a Grenade Travel Faster Than a Bullet?

In the ongoing debate about the comparative speeds of grenade fragments and bullets, many have sought to unravel the truth behind the numbers. This article delves into the physics and calculations that shed light on this intriguing question.

Introduction to the Debate

The television show Mythbusters once explored this question, leading to a fascinating discussion. They used a pinhead-sized bit of metal that was calculated to be traveling at hypersonic speeds, around 20,000 feet per second. This fragment had managed to penetrate bullet-resistant plexiglas, emphasizing its incredible velocity.

Initial Velocity of Grenade Fragments

A quick search into the initial velocity of a perfectly spherical fragment from the composition-B explosive of an American M-61 fragmentation grenade reveals an impressive speed of 480 meters per second (m/s). This velocity is notably higher than that of most pistol cartridges.

Cannonical Example: Comparison with Common Pistol Calibers

Various pistol cartridges, including the .45 ACP and 9x19mm Parabellum, achieve velocities around 10–30 m/s lower than 480 m/s. For instance, the 5.56 NATO cartridge fired from a rifle-length barrel typically attains a velocity of around 500–600 m/s. These figures can be referenced as 1070 miles per hour (mph), providing a sense of the extreme speed involved.

Aerodynamic Constraints and Velocity Loss

While the initial velocity of grenade fragments is indeed remarkable, it's crucial to consider the shape and design of these fragments. Unlike the low-drag-coefficient cylindrical projectiles fired by pistols, grenade fragments often take on a ragged, chunky shape. This design choice impacts the fragment's path, increasing the rate at which it slows down due to aerodynamic drag.

Factors Affecting Initial Velocity

The initial velocity of grenade fragments is determined by several factors, including the heat density per unit mass of the explosive charge, the fragmentation-casing-to-charge mass ratio, and the physical structure of the grenade itself. The shape of the fragment is a key component and can be approximated using Gurney's ratio, which helps in calculating these parameters accurately.

Effect of Aerodynamic Drag

One of the significant impacts on the trajectory of grenade fragments is aerodynamic drag. This resistance force becomes more prominent as the distance increases, causing the fragments to decelerate more rapidly. In contrast, bullets, designed with aerodynamic concerns in mind, maintain their velocity more effectively over longer distances.

Conclusion: The Truth Revealed

Yes, the fragments from a grenade can travel faster than bullets when comparing their initial velocities. However, it's important to consider the physical shape and aerodynamic profile of the fragments, especially in terms of how quickly they lose speed over distance.

Final Thoughts

The unique design and explosive content of a grenade fragment contribute to its initial velocity surpassing that of standard pistol cartridges. However, the slower rate of deceleration for bullets over long distances means that, in practical applications, bullets often outperform grenades in terms of range.

Further Reading

To delve deeper into the topic, kindly refer to the following sources:
- Naval Research Laboratory Report
- ResearchGate: Effects of Fragment Shape on Impact Thresholds