External Ballistics - Understanding Ballistics

8/14/2019 External Ballistics - Understanding Ballistics

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(from the Hornady website)

External Ballistics

Understanding Ballistics

The Hornady Handbook is a practical guide to reloading and shooting. The

ballistics tables presented here provide a comprehensive, readable, and essential

guide to bullet performance. The loads in Volume 1 of the Hornady Handbook tellthe reader how to create great ammo. The tables in Volume 2 explain how that

reloaded ammunition will perform - in the field or on the range - in terms of

velocity, energy, and trajectory.

Many associate the term ballistics with rocket science and become wary of the

whole subject. While you can venture deeply into ballistics in terms of studying

the dynamics of projectiles in general or the flight characteristics of bullets in

particular, you needn't be a rocket scientist to understand and use the

information provided here. Our presentation is pragmatic and practical. Think of

this part of the Hornady Handbook as:

A guide to bullet selection, Instructional advice on sighting in your firearm at different ranges, Detailed descriptions of bullet trajectories at all practical velocities, A rough relative guide to "stopping power" (a bullet's remaining energy), A data base for cartridge selection for different shooting purposes, and The ultimate source of ballistics performance information on Hornady Bullets.

Finally, working with theBallistics Calculator and adjustment factors for varying

shooting environments will give reloaders a better instinctive feel for performancevariables. Over time this will build a high confidence level for every shooter.

Trajectory

OurBallistics Calculator deals with the exterior ballistics performance of Hornady

Bullets. We are not concerned with internal ballistics, the province of the firearms

engineer or powder chemist, nor with terminal ballistics, the province of the

forensic pathologist or other scientific specialists. Terminal ballistics is a veryimportant concern to the military, to police, and to hunters. While there is no way

to model the terminal behavior of all projectiles in all media at all velocities, we'll

mention the subject briefly in the section entitledAn Aside on Energy. For now

we'll focus on exterior ballistics.

A trajectory is a description of the flight path of a projectile relative to some

known and fixed points. Trajectories for BBs, field artillery projectiles, naval gun

shells, mortar rounds, and small arms bullets are all parabolic in shape. In a
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While it makes sense to calculate trajectories for naval shells in terms of angles of

departure and while one could do this for small arms trajectories as well, the

shooter's primary reference in the field is the line of sight. All tables in the

Hornady Handbook are constructed with reference to the line of sight. Telescopic

sights 1.5" above the bore are assumed in line of sight calculations for rifles.

Fixed sights 0.8" above the bore are assumed in line of sight calculations for

handguns.The Ballistic Coefficient

Before discussing this topic in more detail, let's dispel some myths surrounding it.

Whatever you may have heard before, these are the facts:

There is no such thing as an absolute and invariable ballistic coefficient (B. C.) Ballistic coefficients are only one factor in bullet selection for different kinds of shooting. A ballistic coefficient can change with reference to (1) altitude, (2) temperature, (3) atmospheric

pressure, and (4) relative humidity.

Ballistic coefficients are measures of a bullet's relative efficiency. Ballistic coefficients are not measures of a bullet's "goodness." Higher B.C.s do not necessarily make a bullet "better." Lower B.C.s do not necessarily make a bullet "worse."

A ballistic coefficient is the measure of a bullet's relative ability to overcome air

resistance. Each bullet can be assigned a numerical value expressing this

efficiency. The basis of this value is a ratio comparing the performance

characteristics of a particular bullet against the known trajectory characteristics of

a standard projectile. The ratio compares the drag of a bullet (loss of velocity

caused by air resistance encountered in flight) to the drag of the standard

projectile. Expressed as a formula,

Observe that ballistic coefficients in this book are, with only one exception, less

than unity [1.0], indicating that these test projectiles - bullets for small arms -

encountered more resistance than the standard. The single exception in the entire

line of Hornady Bullets is our 50 Caliber (.510" diameter) 750 grain AMAX Ultra

High Coefficient. Its ballistic coefficient is 1.050.

The standard projectile on which all Hornady Bullets were compared was the G1

Model, based on work begun in France and refined at the U. S. Army Ballistic

Research Laboratories, Aberdeen Proving Ground, Maryland. Ballistic coefficients

for all Hornady Bullets were determined by computer calculations using data from

test firing research performed in our 200 yard underground test range.

Ballistic coefficient calculations combine both shape and sectional density factors.

As a practical matter, most shooters understand that bullets with a pointed shape


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more easily retain their velocity than round nose or flat point bullets. This can be

directly observed in the amount of drop bullets of the same weight but different

shapes produce at the same target range. Expressed another way, round nose

and pointed bullets will require different sight adjustments to attain the same

zero over the same range. If more streamlined bullets maintain their velocity

better, heavier streamlined bullets of the same shape will outperform lighter

bullets at the same muzzle velocity.The following examples drawn directly from the ballistics tables in this book

quickly demonstrate the importance of shape to velocity retention and flat

trajectory. We have chosen to compare in this example two bullets of identical

caliber, weight, and sectional density fired at identical 3000 fps muzzle velocities.

Shape is the only variable in this example; all other factors have been held

constant. Observe the marked difference in bullet behavior over the ranges

shown. The round nose bullet sheds its initial velocity faster than the spire point.

Because energy is the product of mass x velocity squared, the round nose bullet's

more rapid velocity loss produces an even faster loss of energy . Mostdramatically, as the less efficient round nose shape loses its velocity, the effects

of gravity show up in terms of greater bullet drop relative to the spire point

bullet. Does this comparison argue entirely against using round nose bullets? By

no means; over the 100 to 200 yard ranges typical of a great deal of hunting, the

round nose holds its own. Moreover, many who hunt with them regard them as

utterly reliable over their intended distances. Confidence counts more than a

lower ballistic coefficient to these folk.

30 CAL. (.308" DIA.) 180 GRAIN SPIRE POINTSECTIONAL DENSITY: 0.271 BALLISTIC COEFFICIENT: 0.425

RANGE (YARDS) MUZZLE 50 100 200 300 400 500

VELOCITY (fps) 3000 2887 2777 2565 2362 2169 1985

ENERGY (ft.-lb.) 3597 3331 3082 2629 2230 1880 1574

100 YD. ZERO -1.5" -0.2" 0.0" -3.0" -11.3" -25.9" -47.8"

30 CAL. (.308" DIA.) 180 GRAIN ROUND NOSE

SECTIONAL DENSITY: 0.271 BALLISTIC COEFFICIENT: 0.241


VELOCITY (fps) 3000 2803 2614 2259 1933 1639 1385

ENERGY (ft.-lb.) 3597 3139 2731 2040 1493 1073 767

100 YD. ZERO -1.5" -0.2" 0.0" -3.6" -14.1" -34.0" -67.0"

Correction Factors

Ballistic coefficients are calculated not only with reference to a standard

projectile, but with reference to standard test conditions as well. All ballistic


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coefficients and ballistics tables in this book have been adjusted to standard

conditions. Altitude=sea level. Temperature=59 Fahrenheit. Atmospheric

pressure=29.53" of Hg. Relative humidity=78%. These are standard conditions

for the Aberdeen test site. What happens when the conditions are not standard?

These four test examples will demonstrate changes in a calculated ballistic

coefficient resulting from varying different test factors in turn.

TEST NO. 1: STANDARD CONDITIONSCONDITIONS: Sea Level, Temperature=59 F, Barometric Pressure 29.53",

Relative Humidity 78%.

RANGE (YARDS) MUZZLE 100 200 300 400 500

VELOCITY (fps) 2900 2627 2371 2129 1901 1690

TRAJECTORY 100 YD.

ZERO-1.5" 0.0" -3.6" -13.3" -30.8" -57.9"

Results: Calculated ballistic coefficient=.338

TEST NO. 2: HIGHER TEMPERATURE

CONDITIONS: Sea Level, Temperature=89 F, Barometric Pressure 29.53",Relative Humidity 78%.


VELOCITY (fps) 2900 2640 2395 2162 1943 1739

TRAJECTORY 100 YD.

ZERO-1.5" 0.0" -3.5" -13.1" -30.1" -56.4"

Results: Due to less dense air (warmer temperatures) the calculated B.C. is

.355.

TEST NO. 3: HIGHER BAROMETRIC PRESSURE

CONDITIONS: Sea Level, Temperature=59 F, Barometric Pressure 31.00",



VELOCITY (fps) 2900 2614 2346 2094 1858 1641

TRAJECTORY 100 YD.ZERO -1.5" 0.0" -3.6" -13.6" -31.5" -59.5"

Results: Due to denser air (higher barometric pressure) the calculated B.C. is

.322.

TEST NO. 4: HIGHER ALTITUDE

CONDITIONS: 10,000', Temperature=29 F, Barometric Pressure 21.00",



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VELOCITY (fps) 2900 2693 2495 2306 2124 1952

TRAJECTORY 100 YD.

ZERO-1.5" 0.0" -3.3" -12.2" -27.6" -50.8"

Results: Due to less dense air (higher altitude) the calculated B.C. is .448.

The .338 calculated ballistic coefficient has ranged from .322 to .448 as

conditions have varied. Common sense suggests that a bullet might perform

better in higher temperatures (less dense air), at lower barometric pressures

(less air pressure), and at higher altitudes (much lighter air). When there is less

air to resist a bullet's flight, it will become more efficient - and conversely. How

can you account for significantly non-standard conditions in preparing, say, for a

major hunt? Assuming that you know the temperature, barometric pressure, and

ballistic coefficient of the bullet you will be shooting in non-standard conditions,

you can calculate the apparent ballistic coefficient of the bullet and otherwise find

the trajectory for your non-standard condition site. The drag on a bullet is largely

produced by the density of the air through which it travels. The first conversion

factor to correct for changes in air density is the ratio of:

Which is used as a multiplier in the correction calculation.

The correction factor for temperature is another ratio, but with a twist:

The 459.4 addition to the site temperature and standard temperature is to place

both in the absolute Rankine Scale. (Absolute zero is -459.4 Fahrenheit or 0

Rankine.) The resulting ratio is also a multiplier in the correction process.

Corrections can be made as well for relative humidity, but the correction process

is tedious and the precision gained is negligible. At any rate, while we've seen

barometers in camp and thermometers on the trail, we can't recall seeing hunterslugging hygrometers. Besides, we have already captured the primary factors

requiring adjustment.

Assume that we encounter the following conditions on a hunt. The temperature is

a chilly 29 Fahrenheit, the barometric pressure 21.00"Hg., and the relative

humidity 85%. Think about this a minute and it seems we're on a mountain hunt

in some very raw conditions. Relative humidity is very close to the standard 78%,

so we'll not worry about adjustments there. But the temperature and atmospheric


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pressure are far from standard. What effect will they have on the ammunition

we've loaded with a standard condition ballistic coefficient of .338?

The Apparent Ballistic Coefficient=Temperature correction factor x Barometric

pressure correction factor x Present ballistic coefficient=.924 x 1.406 x

.338=.448.

The shooter can consult the Hornady Bullet Guide in this book to find a ballistic

coefficient of or near .448 and use the trajectory data presented for that bullet.

As a practical matter, the lower temperature alone would reduce the apparent

ballistic coefficient, but in combination with the low barometric pressure

correction the over all result will be flatter trajectories for the ammunitionbrought on this hunt.

Shooters who go from low altitudes to high altitudes or vice versa should bring

along enough ammunition to sight in their firearms at the new location. The flat

trajectories obtained with reloads in Fort Collins, Colorado may not be so flat on a

hunt in the woods of Maine. Aiming higher over common ranges is the answer

here. Conversely, taking tested loads from Mobile, Alabama to the mountains of

British Columbia may require aiming lower than one might have back home.

For ranges up to and including 300 yards, ballistic coefficient corrections may not,practically speaking, be required. Steadiness of the shooting position and the

aiming skills of the shooter may account for more difference between planned

and actual trajectory than correction factors might require. If actual shooting

conditions are going to be dramatically different from those at home, it's sound

advice to take enough ammunition to re-zero your firearm at the shooting site.

Trajectory Table Applications

Ballistics tables have been an integral feature of Hornady Handbooks from the

first edition on. We spoke earlier of the many benefits they provide the reloader

and shooter. Here we will demonstrate exactly how they can help select bullets

for a particular hunt.

Assume a shooter has acquired a rifle chambered for the 6mm Remington

cartridge and plans to take it on a prairie dog hunt. The shooter has been to this

location before and has the general lay of the land. His targets will present

themselves at ranges of 200 to 400 yards, and hot temperatures there are likely

to stir up cross winds up to 10 mph. What should he load? He'll need a good, flat

trajectory and a bullet that can resist wind drift as much as possible. He narrows


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his choice to three different Hornady 6mm varmint bullets; the 70 gr. Spire Point,

the 75 gr. Hollow Point, and the 87 gr. Spire Point. After reviewing the loading

tables in Volume 1 to see how fast he can push each bullet, he consults the

ballistics tables for these bullets and their top velocities in his rifle.

6 MM CAL. (.243" DIA.) 70 GRAIN SPIRE POINTSECTIONAL DENSITY: 0.169 BALLISTIC COEFFICIENT: 0.269


VELOCITY (fps) 3300 3110 2929 2587 2269 1975 1705

ENERGY (ft.-lb.) 1692 1503 1333 1040 800 606 452

50 YD. ZERO -1.5" -0.0" 0.6" -1.4" -8.6" -22.5" -45.5"

100 YD. ZERO -1.5" -0.3" 0.0" --2.6" -10.4" -24.9" -48.5"

200 YD. ZERO -1.5" 0.3" 1.3" 0.0" -6.5" -19.8" -42.1"

300 YD. ZERO -1.5" 1.4" 3.5" 4.3" 0.0" -11.1" -31.2"

400 YD. ZERO -1.5" 2.8" 6.2" 9.9" 8.3" 0.0" -17.3"

500 YD. ZERO -1.5" 4.6" 9.7" 16.8" 18.7" 13.9" 0.0"

6 MM CAL. (.243" DIA.) 75 GRAIN HOLLOW POINTSECTIONAL DENSITY: 0.181 BALLISTIC COEFFICIENT: 0.294


VELOCITY (fps) 3200 3030 2867 2557 2268 1997 1748

ENERGY (ft.-lb.) 1705 1529 1368 1089 856 664 509

50 YD. ZERO -1.5" -0.0" 0.6" -1.6" -9.2" -23.5" -46.6"

100 YD. ZERO -1.5" -0.3" 0.0" --2.7" -10.8" -20.2" -49.4"

200 YD. ZERO -1.5" 0.4" 1.4" 0.0" -6.7" -20.2" -42.5"

300 YD. ZERO -1.5" 1.5" 3.6" 4.5" 0.0" -11.3" -31.3"

400 YD. ZERO -1.5" 2.9" 6.4" 10.1" 8.5" 0.0" -17.2"

500 YD. ZERO -1.5" 4.7" 9.9" 17.0" 18.8" 13.8" 0.0"

6 MM CAL. (.243" DIA.) 87 GRAIN SPIRE POINT



VELOCITY (fps) 3100 2950 2806 2530 2271 2027 1799

ENERGY (ft.-lb.) 1856 1681 1521 1236 996 793 625

50 YD. ZERO -1.5" -0.0" 0.5" -1.9" -9.8" -24.4" -47.6"

100 YD. ZERO -1.5" 0.3" 0.0" -2.9" -11.3" -26.5" -50.1"

200 YD. ZERO -1.5" 0.5" 1.5" 0.0" -6.9" -20.6" -42.8"

300 YD. ZERO -1.5" 1.6" 3.8" 4.6" 0.0" -11.4" -31.3"


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400 YD. ZERO -1.5" 3.1" 6.6" 10.3" 8.5" 0.0" -17.0"

500 YD. ZERO -1.5" 4.8" 10.0" 17.1" 18.8" 13.6" 0.0"

A common zero - here 200 yards - will enable the varmint hunter to make a

reasonable comparison among his possible choices. All three bullets have

relatively flat trajectories out to 400 yards, the 70 gr. Spire Point dropping least

(19.8") and the others dropping 20.2" and 20.6" respectively below their 200yard point of impact. It would be tough to call this one on trajectory alone.

What about wind drift? How will these three bullets buck cross winds over the

ranges they'll be used? Consulting the Wind Drift Tables at the back of this

volume, the shooter pulls out data for the muzzle velocities he'll load for at the

ballistic coefficients nearest those of the three 6mm bullets.

BALLISTIC COEFFICIENT= .270 (70 grain SP)

RANGE (YARDS) MUZZLE 100 200 300 400

VELOCITY (fps) 3300 2930 2589 2273 1979

WIND DRIFT (in.) 0.0" 1.0" 4.2" 9.9" 18.8"

BALLISTIC COEFFICIENT= .300 (75 grain HP)


VELOCITY (fps) 3200 2873 2569 2284 2018

WIND DRIFT (in.) 0.0" .9" 3.9" 9.2" 17.2"

BALLISTIC COEFFICIENT= .330 (87 grain SP)


VELOCITY (fps) 3100 2808 2535 2278 2035

WIND DRIFT (in.) 0.0" .9" 3.6" 8.6" 16.1"

The shooter notes in these tables that other factors rise to prominence. The 87

gr. bullet starts out 100 to 200 fps slower than the other two, but reaches 400yards with a higher velocity than either. On its flight it stands up better to wind

drift, too. And since it is a heavier bullet travelling at a higher speed at the 400

yard point of impact, it's retained its energy better than its lighter counterparts.

The 6mm 87 gr. Spire Point is a clear choice for his varminting trip.

At what range should he plan to zero his rifle for this hunt? His prairie dog quarry,

as he knows from prior experience, is about 10" high and 2" in diameter. He's

already observed that the 87 gr. bullet will drop 20.6" at 400 yards with a zero at


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200 yards. Holding "two prairie dogs high" at 400 yards leaves a lot of room for

error. With a 300 yard zero, he could hold down less than twice the width of his

200 yard prairie dog target and hold up only about the height of the target at 400

yards. Zeroing at 400 yards would require him to hold under for all ranges less

than the maximum expected. A 300 yard zero seems the best choice.

Changing Zeros

The Hornady Ballistics Tables are an invaluable reference for the shooter whowants to change the zero on his rifle. Everyone does not have access to a range

of 200 plus yards, but may be able to zero in at 100 yards with no difficulty. What

do you do if you will need a 200 yard zero for the hunt you're taking? The shooter

we'll use as an example is using a 30 Caliber 150 gr. Spire Point loaded to a 2700

fps velocity. His solution can't get much easier than this. Consulting the ballistics

table for his bullet loaded to his required velocity, he finds that a rifle zeroed at

200 yards will be 2.2" above the line of sight at 100 yards. The shooter adjusts

his sights to strike 2.2" above his line of sight at 100 yards and he's ready for the

hunt.

30 CAL. (.308" DIA.) 150 GRAIN SPIRE POINT



VELOCITY (fps) 2700 2568 2439 2193 1962 1746 1549

ENERGY (ft.-lb.) 2428 2196 1981 1602 1281 1015 799

50 YD. ZERO -1.5" -0.0" 0.2" -4.0" -15.4" -36.0" -67.9"

100 YD. ZERO -1.5" -0.1" 0.0" -4.4" -16.0" -36.7" -68.9"

200 YD. ZERO -1.5" 1.0" 2.2" 0.0" -9.4" -28.0" -57.9"300 YD. ZERO -1.5" 2.6" 5.3" 6.3" 0.0" -15.4" -42.2"

400 YD. ZERO -1.5" 4.5" 9.2" 14.0" 11.5" 0.0" -23.0"

500 YD. ZERO -1.5" 6.8" 13.8" 23.2" 25.3" 18.4" 0.0"

Sometimes the ballistics tables don't furnish the answers directly but require a bit

of interpolation. Many shooters are anxious about where they should aim when

they're zeroed at a different distance. Suppose the same shooter in the previous

example goes on his hunt with his 200 yard zero only to encounter a target at

250 yards. His bullet will drop 9.4" below the line of sight at 300 yards accordingto the tables. Interpolating between the 200 yard zero and the -9.4" drop at 300

yards, we note that half way between the bullet will have dropped approximately

-4.7". Aiming 4.7" high on the target should produce a dead on hit.

An Aside on Energy

One of the most important benefits the Hornady Ballistics Tables provide is a

significant key to the "stopping power" of different cartridges and bullet/powder

combinations. In our discussion on understanding ballistics tables, we've


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examined the concepts of trajectory, measures of bullet efficiency, the ballistic

coefficient and its derivation, correction factors and procedures for using

standardized ballistics data in non-standard conditions, and trajectory table

applications. We have not focused as much as we might have on the concept of

energy as it pertains to bullet performance and effectiveness.

Over the years many writers have spent considerable time pursuing the concept

of bullet performance. In match competition or target shooting, performancestandards are simple and direct. Bullets for target shooting should be highly

efficient (streamlined, possessing a high ballistic coefficient) in order to shoot as

flat as possible and buck the effects of wind drift. Efficiency counts for naught,

however, if these bullets are not accurate as well - made so carefully and

precisely that they will routinely yield sub-minute-of-angle performance on

targets.

Performance for hunting bullets, however, is a far more complex matter. Some

have contended that you must expect to find your splendidly mushroomed bulletunder the game animal's hide opposite the entry hole. Shame on you if it doesn't

weigh used 95% of what it weighed new. Others have said it's fine if the bullet

enters and exits its target as long as it does deadly damage on its way.

Pragmatists are pleased with bullets that strike where aimed and drop and kill the

game immediately. They are hunters, they argue, not forensic pathologists.

Is performance a matter of opinion only? Of conjecture? A subject like religion

and politics on which there will always be disagreement?

The experienced hunter knows that he will never be presented only with perfect

shots under ideal conditions with his equipment always in superb shape and his

rifle zeroed at the absolutely correct range. That's why the experienced hunter

loves his sport so much. His skill is involved, his judgment is required, his

intelligence is always called for - and he will face real challenges in the field. His

need is to prepare for those challenges, both in his selection of equipment and his

preparation for the field.

Any hunter's odds are greatly improved when he chooses the right gun, the right

bullet, and the right load for the task at hand. This is a point where the energy

calculations in the Hornady Ballistics Tables can be invaluable. As much as ashooter needs to understand such variables as trajectories, the effects of wind

drift, and bullet velocities over anticipated hunting ranges, so, too, must he give

thought to the energy data presented in the ballistics tables to follow.

A bullet's kinetic energy, measured in foot-pounds, is a proxy for what's generally

termed "stopping power." The higher a bullet's energy at the point of impact, it

has been assumed, the greater its "stopping power." There are some caveats

here. A bullet completely releases its energy in the target only if it remains in the


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game animal. If it has more than adequate energy it may do its job and exit. This

is certainly no cause for alarm. If it does not have sufficient energy to bring about

a kill, whether through improper bullet choice or shots at excessive ranges, that

is a cause for alarm. Responsible hunters make sure they can get the job done

with the tools they have chosen. Taking shots at ranges where a bullet cannot

reliably hit and kill a game animal is quite irresponsible behavior.

Hornady Bullets for varminting are designed to fly fast and to release their highkinetic energy instantaneously and explosively. Should they be too powerful for a

particular varmint and pass on through, the wound channel and exit hole will

attest to their destructive power.

Hornady Bullets for game hunting are designed for reliable, controlled expansion

in all hunting bullet designs. No hunting bullet can be as effective as possible if it

does not expand to a larger diameter than its caliber dimension. Expansion slows

the bullet and allows it to shed kinetic energy as it does. All Hornady Bullets for

hunting are made with the InterLock or InterBond features that bind jacket andcore. This assures a heavier mass to penetrate the game animal and propagate

shock waves within it. The higher the terminal velocity of the bullet, the higher its

terminal energy. Expansion and penetration insure energy release which in turn

produces lethal results - and more certain kills.

This is not, nor is it intended to be, the final word on hunting bullet performance.

Rather, we hope to stimulate your thinking about the subject and how important

terminal bullet energies are to performance. Terminal energies and superior bullet

expansion design permit the complete release of a bullet's remaining energy

within the game animal. Hornady Bullets are backed by over 50 years ofexpertise on the subject.

External Ballistics

The firearm itself may be the cause of inaccuracy if the muzzle is burred, if the

throat is eroded in the barrel, or if the trigger is so jerky the shooter cannot

maintain his hold from shot to shot. The stock and action must be properly

bedded to maintain a uniform fit or inaccuracy may result. Even this list does not

exhaust the possible causes of poor accuracy.

A continuous test program is employed to check on our production quality. Ourlaboratory is equipped with the finest test barrels available and with machine

rests which eliminate human variables in shooting so that we can isolate shot-to-

shot dispersion associated only with the bullets being tested.


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The two targets shown in the accompanying

photograph (left) were made firing the same bullets but tested on successive

days. The small group met our accuracy standards and illustrates the kind of

performance we demand of the product. The larger group was fired from bullets

produced after the press making them developed only a few thousandths of an

inch play in its cup feeding mechanism. This evidence of maladjustment brought

the production to a halt so that the press's problem could be analyzed and

corrected.As we said earlier, accuracy doesn't just happen. You have to make it happen, by

paying constant attention to these vital thousandths and ten thousandths of an

inch. No matter how perfect the basic design of bullets may be, they aren't going

to be consistently accurate unless we make them all to closer tolerances than,

say, a Rolls Royce engine.

Perfect balance is perhaps the most critical factor in bullet accuracy. The

attainment of this goal is the major responsibility of design engineers, tool

makers, production personnel and plant management.

They have the task of designing production machinery which will

maintain near-perfect concentricity in the copper cups from which our jackets are

formed in various punch presses. Not only are there multiple steps through whichour copper alloy must pass on its way to becoming a finished jacket, the

concentricity problem is compounded by our need to internally shape the jacket

to control expansion in our hunting bullets (right, above). If the finished jacket is

not of uniform thickness around its entire circumference, if it varies by even so

little as five ten thousandths of an inch, the resulting bullet may be unbalanced

sufficiently to veer from its intended line of flight.


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In the accompanying drawings we will let the green dot

represent the center of form of this bullet, a point at the actual dimensionalcenter of the bullet. The red dot indicates the center of gravity of the bullet; both

of these points should coincide exactly (A).

But because the jacket of this bullet was made with a thinner wall on one side,

there is more lead there (B) and the center of balance is moved ever so slightly in

the direction of the heavier side, perhaps less than a thousandth of an inch (C).

As long as the bullet is in the barrel it rotates around its center of form (D) but

when it leaves the barrel it spins around its center of gravity (E) and this causes

it to veer slightly off its intended course at a tangent to the spiral described by itscenter of gravity as it went up the bore.

Less than half a thousandth of an inch in jacket concentricity can and does have a

detrimental effect upon a bullet's course. And because we cannot chamber each

bullet with its center of gravity similarly aligned in the barrel, subsequent shots

will diverge at arbitrary angles, slight though they may be. The final result is a

group with more dispersion than we would like.


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It is only by minding all those ten thousandths of an inch and tenths of grains in

all stages of production that we are able to make millions of bullets capable of

exceptional accuracy and in a variety of calibers having expansion characteristics

suitable for target, varmint, and big game hunting.

We believe shooters need and want the kind of accuracy we've discussed in this

short essay. That's why the people at Hornady Manufacturing take accuracy so

seriously. The effort to produce accurate bullets, to make accuracy happen, is ajoint effort involving many individuals, their skills, and their dedication to the final

goal.

Doing your shooting with super accurate and effective cartridges which you

yourself have loaded not only provides more shooting for your money but better

shooting. The accuracy factors that we discussed early in this section have

indicated why it is possible to make better ammunition than you can buy.

And reloading can also give the shooter an invaluable sense of pride in his own

craftsmanship. It's the same pride that we at Hornady Manufacturing share inproducing quality products which can be used confidently and effectively.

External Ballistics - Understanding Ballistics

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Transcript of External Ballistics - Understanding Ballistics