.22 Long Rifle cartridge Exterior Ballistics and Wind Drifts

8/14/2019 .22 Long Rifle cartridge Exterior Ballistics and Wind Drifts

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.22 Long Rifle Exterior Ballistics

Ever wonder what the trajectory of a 22 Long Rifle bullet looks like? I often have, especiallwhen trying to sight in a rifle. In this series of articles you'll find "thought experiments"conducted with the help of computer software that, among its many useful features, can

predict the path, or trajectory, of a bullet in flight.

Covered subjects include bullet drop, wind deflection, and the effect of scope cant.

Exterior BallisticsWind Drift: Cross WindWind Drift: Head On WindScope Cant

This page covers how bullet drop varies with distance, and attempts to shed some light on

optimum sight settings. Later I'll look at the effect of wind on bullet drift.

How far above point of aim at 25 yards would you sight in your favorite squirrel rifle to staywithin a 1" circle with a dead on hold? What would the drop be at 100 yards with thatsighting? How many rounds at the range would it take to come up with answers to thesequestions?

Take it from me, it is far easier to calculate the answers with a modern computer program.use Jim Ristow'sGun Controller V2.2.7 to take a look at trajectories for Federal's AmericanEagle discount load, as well as the premium UltraMatch subsonic cartridge. Here's what I

found out.*

Gun Controller requires a ballistic coefficient to perform its calculations, but not one of thehalf dozen ammunition catalogs I reviewed had published that information. Fortunately, GuController has the capability to determine the ballistic coefficient from range data. Federal'catalog lists velocity data for 25, 50, 75, and 100 yards, making this calculation very easy.

Table 1 below shows the trajectory results for the American Eagle bargain load, typical ofmost dime store 22 ammo that sells for about $2 a box. I assumed that I was going after atarget with a 1" diameter vital zone, and asked Gun Controller to determine the optimum

sighting in distance so that I could hold dead on the target and still hit within the 1" circle.
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Table 1. Trajectory of a typical 22LR high velocity cartridge.

From looking at the table, it might surprise you to see the bullet starting off 1.5" below theline of sight, but remember that the scope is 1.5" above the center line of the rifle bore. Atabout 12 yards, the bullet crosses into the bottom of our 1" circle, and at 25 yards is .2"above the circle center. When the bullet reaches 40 yards it is at the top of the circle, and aabout 67 yards the bullet falls out the bottom of the circle. Way out at 100 yards, the bullet

is about 4 3/4" low. Figure 1 shows the trajectory.


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Figure 1. Trajectory plot for 22 Long Rifle high velocity load.

We can do the same thing for Federal's subsonic target load. Match shooters favor this loabecause the turbulence that accompanies transitioning through the sound barrier is absen


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Table 2. Trajectory of a 22 Long Rifle subsonic cartridge.

The slightly lower velocity shifts the midpoint trajectory and circle crossing points closer tothe muzzle: 35 yards at circle top, about 57 yards at circle bottom, and .32 high at 25 yards

At 100 yards, the load is down more than 7 inches. The 25 yard distance is actually higherthan that of the high velocity load in order to compensate for the lower velocity. And the

range within which a dead on hold is good goes from 54 yards with the high velocity load toabout 49 yards with the target fodder. At 100 yards the high velocity load is down by about4 3/4", while the target ammo drops 7".

These figures will be close for most rifles (including 10/22 rifles) shooting high velocity andsubsonic loads. Federals velocity data was obtained with a 24" test barrel. Velocity for the22 Long Rifle peaks with barrel lengths of about 20 inches, and actually drops off withlonger or shorter barrels. Test barrels usually have chambers cut to minimum dimensions,which tend to produce slightly higher velocities than those found in sporting or even target


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arms. These two factors work against each other for Federal's setup, but may not entirelyoffset each other. The difference between these calculated trajectories and those obtainedwith your rifle will, however, be fairly small.

Figure 2. Trajectory plot for 22 Long Rifle subsonic load.

The tables above also contain drift data calculated for a 15 mph wind crossing the bulletpath from the left at 90 degrees. The data also shows the lead necessary to hit a targetmoving from right to left at 10 mph. Since the target is moving into the wind, the bullet pathfirst leads the target, then falls behind it as distance increases. Under these conditions, ittakes a lead of almost 4 feet to hit the target at 100 yards. Now that would be some shot!

.22 Long Rifle Wind Drift: Cross Wind

After considering how far a 22 Long Rifle bulletdrops as distance increases, it was onlynatural to wonder how much effect wind had on group size. The ranges available here inthe San Francisco Bay Area are never calm, and even on the best days feature ten tofifteen mph breezes, with gusts up to twenty-five. Worse yet, the direction is seldom
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constant, as most of the ranges are situated in canyons and hills that bend and distort whamight otherwise be steady on-shore winds. A light 10 mph breeze doesn't feel like much,but best groups hovered near the half inch mark at 50 yards. No matter what ammunition ohow good the trigger pull and barrel, that half inch barrier seemed unbreakable. Could suca light wind really make that much difference? It was time to break out Jim Ristow'sGunController (V2.2.8) once again to take a look at wind drift for Federal's American Eaglediscount load, as well as the premium UltraMatch subsonic cartridge. Here's what I found

out.

Starting with the Federal economy load and a 10 mph wind crossing from the right, Table 1shows that the deflection at 50 yards would be close to an inch.

The calculation assumes that the wind is steady for the entire 50 yards, which owing to thegusty nature of local breezes is somewhat optimistic. But if the wind speed varied betweenzero and five mph, drift would spread between zero and one inch. The best group sizeunder such conditions, if no allowance for wind was made, would be one inch, and woulddepend on the rifle having zero deviations, and the rifleman making every shot perfectly.

Figure 1 shows a plot. Note that at 100 yards, deflection increases to more than 5inches!
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Table 1. Wind Deflection of a typical .22LR high velocity cartridge.


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Figure 1. Wind Drift plot for 22 LR high velocity load.

It is starting to look like shooting sub MOA groups in conditions like this would take amiracle, no matter how well tuned the rifle, or how much magnification was available withthe scope. But maybe there is better ammunition available than the bargain stuff.

Table 2 shows what happens when we switch to subsonic ammunition. A first guess withofirst looking at the table would be that deflection would increase, but such is not the case.


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Table 2. Wind drift of a 22 LR subsonic cartridge.

According to Jim Ristow, author of Gun Controller, deflection undergoes some unusualchanges near the speed of sound. In Jim's words: "When a 22 is fired within the"Transitional Zone" air drag is minimal until it starts exiting the "Zone".

While you would think there should be deflection at the start of a 22LR trajectory, physicssays no 'cause the bullet is nearly being fired in a vacuum. This is why higher muzzlevelocities produce more deflection and why Chuck Yeager's ride was rough when trying toget TO the speed of sound, then immediately smoothed out as he crossed it. If you considehis plane a projectile, just accelerating rather then decelerating, you get the idea." Jim goeon to say that most ballistics programs go bananas when asked to compute deflection forsmall projectiles traveling at speeds near the speed of sound. They predict negativedeflection (bullets deflecting up wind!), or just plain bomb. Indeed, Jim has made specialadjustments to Gun Controller to account for the phenomena. The bottom line, though, isthat the calculations are most useful for comparison between loads and condition sets, and


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actual deflection may differ from the calculations. In this case, deflection at 50 yards in thesame 10 mph cross wind drops by .05" for the subsonic round, a difference hardly worthmentioning. Figure 2 shows the wind drift plot for the subsonic loading.

Figure 2. Trajectory plot for 22 LR subsonic load.

If you're shooting a 22 long rifle in even light wind, you don't have too far to look for an alibwhen all your bullets don't all go into one hole. As these tables and charts show, a breeze ust 10 mph can blow your shot by an inch at 50 yards. And if you shoot in variable winds,as most of us do, a 2 MOA (1") group is the best you can hope for even with a rifle that

shoots like a laser, unless you know how to compensate for wind drift, and consistentlyudge wind speed.

.22 Long Rifle Wind Drift: Head On Wind

If a 10 mph cross wind can deflect a 22 Long Rifle bullet almost one inch at 50 yards, whatchange in impact point is due to the same velocity head on (blowing toward the shooter


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from the target) wind? Again, Gun Controller can help find some answers.

Table 1 shows that the bullet will hit .12" high at 50 yards. Looking back to theplots shot instill air,the impact point would be .35" high at 50 yards. That's a change of almost 1/4"! Nwonder those BR50 shooters use so many wind flags!

Table 1. Trajectory of a typical 22LR subsonic cartridge in head on wind.
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Figure 1. Trajectory plot for 22LR subsonic load in head on wind.

Figure 1 above tells us that the bullet drops almost 7" at 100 yards, an increase of morethan 2" over theshots made in still air.

.22 Long Rifle and the Effect of Scope Cant

Scope what? Scope Cant describes the tipping or tilting of the rifle and scope to one side othe other of verticle. Very small devaitions from straight up make surprisingly large changeto impact point. To find out just how large, I once again turned to Jim Ristow'sGunController V2.2.8.

The Exterior Ballistics portion of Gun Controller has a function that allows introduction of asight cant error. Sight cant is measured in degrees, with 6 degrees equal to the slant of theminute hand as it points to 12:01 on an old style analog clock. One minute of tip isn't muchand it would be easy to miss it when looking through the cross hairs, especailly if there weno horizontal or vertical references visible.
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Table 1 shows that the bullet starts off .16" to the left of the line of sight, just as you wouldexpect if the scope was tipped to the right. The bullet crosses the line of sight at about 30yards, and by the time it arrives at 50 yards, its 1/4" right of the aiming point.

Table 1. Trajectory of a typical 22LR subsonic cartridge showing the effect oscope cant.

Figure 1 shows the plot of the deflection data from Table 1.


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Figure 1. Trajectory plot for 22LR subsonic load showing the effect of scopecant.


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.22 Long Rifle cartridge Exterior Ballistics and Wind Drifts

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