What is a Keyhole Shot?

A keyhole shot, also widely known as keyholing, occurs when a bullet tumbles end-over-end in flight rather than maintaining its stable, point-first trajectory. This instability causes the bullet to strike the target sideways or at an angle, leaving an elongated, oblong, or "keyhole" shaped hole in the paper target, distinct from the clean, circular hole made by a stable bullet.

This phenomenon is a clear indicator that the bullet is not spinning sufficiently or correctly to maintain gyroscopic stability throughout its flight path.

Understanding Bullet Stability

For a bullet to fly accurately, it needs to spin rapidly along its longitudinal axis, much like a football thrown with a spiral. This spin is imparted by the rifling (grooves) inside the barrel of a firearm. When this spin is insufficient or disrupted, the bullet can become unstable and begin to tumble, leading to a keyhole shot.

Common Causes of Keyholing

Several factors can contribute to a bullet losing stability and causing keyholing:

• Incorrect Rifling Twist Rate:
  • Too Slow: If the barrel's rifling twist rate is too slow for the bullet's length and weight, it won't impart enough spin to stabilize the bullet. Longer, heavier bullets generally require faster twist rates.
  • Too Fast: While less common for causing keyholing, an excessively fast twist rate can sometimes over-stabilize very light or short bullets, potentially leading to issues, though instability manifesting as keyholing is rare in this scenario.
• Worn or Damaged Barrel: A barrel with worn-out rifling, especially near the muzzle, or one that is damaged (e.g., from excessive cleaning rod use or impacts), may not impart consistent or sufficient spin to the bullet.
• Improper Ammunition:
  • Incorrect Bullet Weight/Length: Using bullets that are too heavy or long for the firearm's specific twist rate.
  • Damaged or Deformed Bullets: Bullets that are deformed before or during the firing process can fly erratically.
  • Underpowered Loads: If the bullet leaves the barrel at a velocity too low for the rifling to effectively stabilize it, it can tumble. This is more common with handloaded ammunition.
• Excessive Fouling: Heavy build-up of lead or copper fouling in the barrel can reduce the effectiveness of the rifling.

Implications of a Keyhole Shot

Keyholing is more than just an unsightly target hole; it signifies significant performance issues:

• Severe Accuracy Loss: The primary consequence is a drastic reduction in accuracy. A tumbling bullet cannot maintain a predictable trajectory, making precise shooting impossible.
• Reduced Terminal Performance: For hunting or defensive applications, a tumbling bullet may not penetrate or expand as designed, severely compromising its effectiveness.
• Indication of a Problem: It serves as a critical diagnostic sign, alerting the shooter to a potential issue with their firearm, ammunition, or reloading practices.

Troubleshooting and Solutions

If you observe keyholing, here are steps to diagnose and potentially resolve the issue:

• Inspect Your Barrel: Carefully examine the barrel for signs of wear, pitting, or damage, particularly the rifling at the muzzle.
• Clean Your Firearm Thoroughly: Remove any lead, copper, or carbon fouling from the barrel.
• Experiment with Ammunition:
  • Try different bullet weights and types to find one that stabilizes well with your firearm's specific barrel twist.
  • Test ammunition from different manufacturers.
• Check Muzzle Velocity (for Reloaders): Ensure handloaded ammunition is developing sufficient velocity for bullet stabilization.
• Consult a Gunsmith: If basic troubleshooting doesn't resolve the issue, a professional gunsmith can assess the barrel and recommend further action, which might include rebarreling.

Keyhole Shot Analysis