Over time—and especially more recently, with long-range shooting becoming increasingly popular—we have come to realize that a large segment of the shooting community is either unaware of, or chooses to ignore, the importance of selecting the correct bullet for their particular barrel.
Different manufacturers use different barrels, but more importantly, they often use different twist rates. This is the single most important factor that should guide you in choosing the most suitable bullet weight for your barrel.
By "best bullet," we don’t necessarily mean the brand of the bullet, but rather the weight of the bullet.
The only way to make, for example, a 6mm calibre bullet (with the same shape) heavier is by making it longer, since the diameter must remain the same. The other way to make a bullet heavier without making it longer is to change its shape.
Let’s assume:
- Bullet A is a very streamlined bullet, 25mm long, with a pointed nose and boat-tail base, weighing 87 grains.
- Bullet B is also 25mm long, but with a round nose and flat base, weighing 95 grains—all because of the shape.
Since both bullets are the same length, they will stabilize equally well in the same twist rate barrel at the same velocity.
Clarifying Bullet Design and Stability
Take, for example, a 6mm bullet weighing 87 grains with a very aerodynamic shape—typically called a VLD (Very Low Drag). This type of bullet will be long and streamlined, with:
- a slow tapering ogive (nose section), and
- a boat-tail base (tapered, not flat).
These design features are incorporated to create a bullet with a high ballistic coefficient (BC)—a value that expresses the bullet’s ability to overcome air resistance.
Let’s assume this bullet has the highest BC of all 6mm calibre 87-grain bullets. That means it will have the flattest trajectory and the least wind drift of all 6mm 87-grain bullets if all are fired at the same velocity from the same rifle.
How Bullet Stability Works
Bullet stability is achieved in two ways:
- Barrel twist rate (the most important factor), and
- Velocity (the speed at which the bullet is launched).
The longer a bullet becomes—for example, a 95-grain VLD bullet measuring 29.5mm—it requires more spin (rotation) to be properly stabilized.
The only ways to achieve this are:
a) Using a barrel with a tighter twist rate, or
b) Increasing velocity, which also increases rotational speed.
However, velocity can only be increased safely up to the maximum allowable pressure. If the bullet is still marginally stable—or outright unstable—after reaching safe maximum pressures, it means the twist rate is too slow for that particular bullet, and it is not suited for use in that barrel.
The Effects of Poor Bullet Stability
One of the main side effects of poor bullet stability is excessive yaw—when the bullet’s base oscillates in a spiral relative to the nose. A properly stabilized bullet spins cleanly, with both base and nose aligned on the same axis, producing very little yaw that quickly disappears after leaving the barrel.
Other factors that can reduce bullet stability include:
- Air density: Cold, dry air (which is denser than warm air) can further destabilize a bullet. A bullet that is marginally stable on a warm, calm day might become completely unstable in cold conditions, sometimes failing to even reach the target at longer ranges (e.g., 300m).
- Wind: Wind can greatly worsen the destabilization of a bullet already suffering from excessive yaw.
When you combine these environmental factors with a barrel twist rate that is too slow for the chosen bullet, the result is poor—or even nonexistent—accuracy.