What Drives .22LR Accuracy?

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grauhanen

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What Seems Like Oddities as a Starting Point

When using a chronograph, shooters can often see two rounds from the same lot with the same MV have different points of impact (POI). They may see two rounds with different MVs have the same POI. Same rifle, same conditions.

Careful tracking of round MV and POI can confirm that MV/POI mismatch occurs regularly. Shots with the same muzzle velocity can produce different points of impact, while shots with different muzzle velocities can land in the same place. It is also possible to see faster rounds strike lower than slower ones at short range.

This does not refer to isolated occurrences. They happen regularly. They become very obvious when the distance reaches 100 yards.

Intuition may tell shooters this should not happen. But it does. Intuition can mislead. Here it’s often based on velocity differences alone. It’s not faulty intuition; it’s just not more fully informed intuition. *

If velocity alone determined the result, these apparent oddities would not occur.

There is more going on than simple “flight after the muzzle.” The shot is already different before it gets there.

This must mean that what’s on the target is governed by more than post-muzzle trajectory.

The launch condition matters, and so does what happens immediately after launch.

This thread aims to explain both.

*Many shooters may recall when they intuitively thought faster .22LR bullets must drift less in wind than slower ones. That intuitive thinking was not as fully informed as necessary. In the past I've relied on intuitive thinking far too much.

I will be making a number of posts. You may wish to see them all before posting a response.
 
Each Shot Has Two Phases: Launch and Flight

A helpful way to picture rimfire accuracy is to separate two phases.

The first is the launch phase: everything that determines the bullet’s direction and initial condition at the instant it leaves the barrel.

The second is the flight phase: everything that happens after the bullet is in free air.

Many discussions focus almost entirely on flight. That works well only if launch is stable and repeatable.

In rimfire, launch is not automatically stable. And even when the launch condition is good, the bullet’s imperfections still affect what happens immediately after it leaves the muzzle.

Accuracy therefore requires both: a repeatable launch condition and a bullet that behaves consistently once free. Without them, the flight becomes unpredictable.
 
Velocity is Necessary, but Not Sufficient

Velocity sets the initial time scale of the shot.

A faster bullet reaches the target sooner. A slower bullet takes longer. Since gravity acts during flight, the amount of drop depends on how long the bullet is in the air.

This explains why velocity variation produces vertical spread. It is real, measurable, and always present.

But it is not enough.

If velocity alone controlled impact location, then shots with equal velocity would strike together and shots with different velocity would separate consistently. That is not what shooters observe.

Velocity is one part of the explanation. The mismatch between velocity and impact is the evidence that other factors are involved at the same time.
 
The Muzzle is Not Fixed in Direction – It does not always point in exactly the same direction

At the instant the bullet exits, the muzzle has a specific direction. It is no longer fixed. That is because, once the shot is fired, the muzzle begins to move due to the forces generated during firing and the wave pattern moving through the barrel.

Think of a wave pattern traveling along the barrel. The end of the barrel, the muzzle, must move in response. This motion is extremely small and not visible to the human eye, but it is real and measurable. The muzzle typically moves in an elliptical pattern.

At the moment the bullet exits the muzzle, the launch angle corresponds to the direction the muzzle is pointing (the muzzle angle).

That direction defines the initial trajectory of the bullet.

The important point is that the muzzle is not perfectly stationary. The firing event produces forces that cause the barrel to move. The bullet exits during that motion.

Even extremely small differences in muzzle direction produce measurable changes downrange. As distance increases, a small angular difference becomes greater point‑of‑impact separation on the target.

This is the second contributor that explains why velocity alone does not determine point of impact.

Launch angle is a key driver of trajectory and where the point of impact will be.
 
Putting it Together – What does it Mean

Barrel Motion and Timing – The Launch Angle

When a round is fired, the barrel bends and vibrates. This motion is not random. It follows a consistent pattern, repeating the same general movement every time the rifle is fired.

What changes from shot to shot is not the pattern itself, but the timing of events within that pattern.

The bullet does not exit instantly. It takes a small but very real amount of time to travel from the chamber to the muzzle. During that time, the barrel is already moving.

This leads to an important consequence.

If two bullets take slightly different amounts of time to travel down the barrel, they will exit at slightly different points in the barrel’s motion. Even if the difference is extremely small, the muzzle may be pointing in a slightly different direction at the moment each bullet leaves.

That difference in muzzle direction is the launch angle.

Timing controls where the bullet exits within the barrel’s motion.
The exit point determines the muzzle angle.
The muzzle angle determines where the shot goes.

This connection is what ties velocity, barrel behavior, and point of impact together.
 
Same MV, Different Launch Angle – Why This Happens

At this point, intuition may mislead. It did for me.

If two rounds have the same muzzle velocity, they must have experienced the same conditions and therefore leave at the same angle.

That assumption is incorrect.

Muzzle velocity tells us only the final speed at exit. It does not describe how the bullet reached that speed. That part of its journey can differ and refers to internal ballistics.*

Inside the barrel, the bullet is accelerated by a pressure that changes continuously during the shot. Because of this, there is not a single path to a given muzzle velocity. Different internal conditions can produce the same final speed.

This means two rounds can reach the same muzzle velocity but not take exactly the same time to reach the muzzle.
Even very small differences in internal behavior such as ignition, pressure progression, or friction can slightly change the time the bullet spends in the barrel.

That time difference places each bullet at a slightly different point in the barrel’s motion at the instant of exit.

Same muzzle velocity.
Different exit timing.
Different muzzle direction.
Different launch angle.


*Internal ballistics is a time-dependent process (pressure, acceleration, velocity all vary over time). While there’s no specific data about the variation available to the public, such variations are established principles in ballistics and are not controversial. We know that they vary and that’s what matters.
 
Velocity matters, but indirectly

Velocity matters here, but not in the way it is often assumed.

Its primary role is to influence how long the bullet remains in the barrel. A faster bullet exits sooner. A slower bullet exits later. That change in timing shifts the exit point along the barrel’s motion.

The result is a different launch angle.

This is why changes in velocity do not translate directly into predictable vertical movement on the target. The effect depends on where in the barrel’s motion the bullet happens to exit.

If the muzzle is moving rapidly at that moment, small timing differences produce larger changes in angle. If the muzzle is moving slowly, the same timing differences produce smaller changes.

The system is sensitive to timing, not just to speed.

What you see on the target is the accumulated effect of many small variations in when each bullet leaves the barrel relative to its motion.

Shots are not leaving under identical conditions. They are leaving at slightly different moments in a moving system.
That is what drives launch angle variation.

And that is why small differences at the muzzle turn into visible differences on the target.
 
What Happens After the Bullet Exits the Muzzle?

Once the bullet gets out of the barrel muzzle, its trajectory is not pre-ordained. That means that it is not simply the product of the launch angle and its MV. Other factors help shape how the bullet flies downrange.

The bullet’s path is controlled by gravity and air resistance (drag). Gravity is fixed and unchanging. It affects all bullets, fast or slow. Drag is affected by the bullet itself and can change.

The .22LR bullet is an imperfect thing. Not all are identical.
 
Problems of .22LR Bullet Integrity

Bullet Center of Gravity and Heel Variation

Bullet perfection in shape, geometry, and form are about bullet integrity. The problem is that .22LR bullets rarely have perfect integrity.

Even within the same box, small differences exist in balance and geometry. The center of gravity may be slightly offset, and the heel—the part that fits into the case and the most delicate part of the bullet—may vary slightly in shape or alignment.

Soft lead projectiles like .22LR bullets are swaged. Unlike jacketed centerfire bullets, .22LR bullets are difficult to manufacture with nearly perfect centers of gravity. When the Cg is offset, it disturbs the bullet’s trajectory. Cg can vary from lot-to-lot, even between bullets. Some barrels may add to Cg imperfections by the unique obturation their leade and bore.

The base of the bullet, the heel, is the last surface influenced before flight begins If the heel is imperfect, if the base is not uniform, it has more influence on bullet trajectory than bullet nose imperfection.

The base of the bullet is the last surface influenced before free flight begins.

As the bullet exits, high-pressure gas flows past the base. This flow must be symmetrical for the bullet to be released cleanly. When the base is not uniform, gas escapes unevenly and this can cause a small disturbance as the bullet exits.
 
These differences are small, but they affect how the bullet behaves in flight.

A more uniform bullet tends to move through the air more predictably. A slightly imbalanced or irregular bullet experiences small differences in drag, which changes how it slows down and how long it takes to reach the target.

That difference in time of flight produces differences in drop.

At short distances, the effect is small and not significant. As distance increases, however, it becomes more visible.

This is the second half of the system. Launch determines direction. Bullet behavior in flight determines how those directions separate.
 
How the System Works Together – Launch Angle and Bullet Flight

Rimfire accuracy is the result of two mechanisms working at the same time.

Launch sets the starting direction of each shot. Flight determines how those shots separate as they travel.

Each shot leaves the barrel at a slightly different angle. At the same time, each bullet behaves slightly differently in flight due to small variations in drag.

These effects do not act independently. They combine.
A shot that starts slightly high may lose more speed and drop back toward the group. Another may retain speed and continue separating. A third may combine both effects.

The target reflects all of these at once.

Group shape is not the result of one cause. It is the visible record of the interaction between how shots are launched and how they behave in flight.
 
Why Groups Get Worse With Distance

The causes of dispersion are already present at the muzzle.

As distance increases, those same causes simply have more distance over which to act. A small angular difference produces a small separation at short range, but a larger separation at longer range.

The same applies to flight behavior. Small differences in drag have limited effect at short distances, but as time-of-flight increases, those differences accumulate and become more visible.

Nothing new is introduced at distance. The system has not changed. The same differences are simply carried farther.

This is why results can appear stable at 50 yards and more erratic at 100. The variation was always present—it has simply become easier to see.

Distance magnifies.
 
The Barrel Does Not Create Quality, It Preserves or Disturbs It

This is where precision matters in wording. It should not be misunderstood.

A barrel does not arbitrarily make good ammunition perform badly. What it does is determine how consistently each bullet is launched.

Two things exist:
  • the inherent variation in the bullets
  • the consistency of the barrel in handling them

A high-quality barrel:
  • applies more consistent conditions to each shot
  • minimizes additional disturbance

A lower-quality barrel:
  • introduces more variation in launch
  • amplifies the variation already present in the bullets

Good ammunition performs well when it is launched consistently.
 
The Rifle/Barrel/Ammo System Is Interactive, Not Independent

The result on the target is not produced by one factor acting alone.

It is produced by the interaction of the following:
  • velocity differences
  • launch direction differences
  • bullet condition differences
Velocity affects timing. Timing affects launch angle. Bullet condition affects both initial disturbance and flight behavior.

All three are present in every shot.
 
The Basic Idea or Model That Explains What You See on Target

Every shot is defined by three conditions at muzzle exit:
  • Velocity determines how long the bullet remains in flight.
  • Launch direction determines the initial path of the bullet.
  • Bullet condition or integrity determines how consistently the shot is launched and how the bullet behaves in flight.
The variation shooters see comes from small differences in those three conditions.

The mismatch between velocity and impact is not an anomaly. It is the expected result of a system where multiple factors act together.

Once those factors are understood, the behavior is no longer confusing. It becomes predictable in principle, even if it is not perfectly measurable shot by shot.

What changes from rifle to rifle, and from lot to lot, is not the existence of variation. It is how much variation is present, and how the system responds to it.
 
The Final Takeaway in Brief

Rimfire accuracy is not primarily a velocity problem. It is a launch-and-flight problem.
  • The barrel determines how the bullet is launched
  • MV determines when that launch occurs
  • Bullet quality (CG and heel) determines how the bullet behaves in flight
  • Distance reveals and amplifies all of these effects

With rimfire always remember that what's intuitive may need to be reconsidered.
 
Very interesting thread. Although I am not a rimfire competitor, I do shoot cast bullets for accuracy. One thing I might add. Cast lead bullets are fragile and as far as I can tell, significant distortions to the bullet can happen in the process of the bullet leaving the case and transitioning through the chamber's throat. This can easily be seen by those of us who shoot in the old style of breech seating cast bullets. Although this doesn't help rimfire shooters much, removing this problem by carefully breech seating the bullets has a marked effect on accuracy. These distortions are, I believe, the largest problem with cast bullet accuracy. Interestingly F.W. Mann wrote about a lot of this long ago, although his methods were not particularly rigorous.

Thanks for the interesting thread.
 
all of the above and...
head spacing is what I look for, the rim depth sets the head space on a .22

why is a .357mag more accurate than a 9mm? head space is repeatable better with the .357mag
 
There has been extensive use of barrel tuners, heavy barrels with choke bores and thicker diameter the last 6 inches, in rimfire competition for decades. All of these are designed primarily to offset or reduce the effect of the barrel harmonics/direction as the bullet leaves the barrel. Match chamber, many that are ammo specific, using top quality ammo addresses the velocity variance as well as consistency of the bullet and consistent ignition. You posted some great info, but failing to provide the actual solutions seems to be a miss, easily rectified.
 
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