Wear and Tear on Rifle Barrels: Can You Actually Wear Out the Rifling?
Understanding the Forces Involved in Rifling and Barrel Erosion
When it comes to firearms, the principle of rifling is fundamental to ensuring accuracy and reliability. Rifling refers to the precision grooves inside the barrel that cause the bullet to spin, improving its stability in flight. However, this process also involves immense forces and temperatures. Let's delve into the mechanics of rifling and the extent to which barrel wear and tear can impact its functionality.
How Rifling Ensures Precision and Gas-tight Seals
The forces involved in driving a bullet down a barrel and forcing it to spin at extremely high speeds are tremendous. To prevent the burning propellant gases from leaking past the bullet, the bullet must fit the rifling to a precise degree. Typically, jacketed bullets are made slightly oversized, measuring 0.001 inches or 0.00254 millimeters larger than the barrel diameter. This ensures correct engagement with the rifling and creates a necessary gas-tight seal.
It's worth noting that the softness of the bullet jacket means that most erosion or wear is borne by the bullet, not the barrel steel. However, even with these protective measures, rifling can still experience wear over time due to the immense forces and temperatures involved.
Measuring Rifling Wear: Go-No-Go Gauges
To measure and quantify barrel wear, gunsmiths and military armourers use go-no-go gauges. These are precision machined metal cylinders of slightly increasing diameter. If a gauge machined to the tolerances of a new barrel can drop down the barrel, it indicates wear. By using the next larger gauge, one can determine the degree of wear by comparing it against the bore of the barrel.
When the largest gauge that indicates the maximum acceptable wear fits the bore, the barrel is declared worn or 'shot-out' and requires replacement. This method is particularly crucial for military and high-fire-rate firearms, where barrels can overheat to almost red-hot conditions.
Barrel Overheating and Rapid Fire Rates
The rapid fire rates of some military firearms can lead to barrels overheating dangerously. For instance, the German MG-34 has a rate of fire of 800-900 rounds per minute, while the MG-42 can fire an average of 1,200 rounds per minute, with the ability to reach 1,500 rounds per minute under optimal conditions. This means that even a few minutes of intermittent firing can lead to barrels overheating to potentially hazardous temperatures.
Military operators often carry multiple barrels, changing them as they cool to prevent barrel failure from overheating. This practice helps maintain accuracy and safety, but even with frequent barrel changes, the rifling can still sustain some wear over time due to the repeated high-temperature conditions.
Conclusion
While the thin bullet jackets protect the barrel steel from direct erosion, rifling wear is inevitable due to the immense forces and temperatures involved. Measuring wear using go-no-go gauges is essential for ensuring barrel reliability and safety. Rapid fire weapons like the MG-34 and MG-42 highlight the importance of barrel management to prevent overheating and potential failure. Understanding and managing barrel wear is crucial for maintaining the accuracy and functionality of rifles and sub-machine guns.