The following page is a lengthy one but it is quite essential to work through if it comes to choice of caliber. If you are unsure of which caliber will give you the desired results for your shoot, the information below will be a great help to you.

Contents of this Page

Internal Ballistics, the Barrel and the Bullet.
Length of the Barrel.
External Ballistics, the Bullet in Flight.
Ballistic Coefficient (Bc) or The Streamline Quality of the Bullet
Terminal Ballistics
Penetration
Our Formula for Penetration.

 

INTERNAL BALLISTICS, THE BARREL AND THE BULLET.

The barrel of a gun has one function and that is to guide the bullet to the target but needs specific detail to be able to achieve what is aimed for.
Firstly rifles had smooth barrels and a spherical bullet was pushed down the barrel wrapped in a cloth or paper patch, which helped to seal off the gasses from passing the bullet. Col. Boxer used a tapered wooden plug that was forced into the hollow bullet by the expanding gas to increase the size of the bullet and sealed of the gasses.
We read that the first rifled barrel was the result of bad workmanship but proved to be more accurate. Rifling was then cut with an angled blade that, when pushed down the barrel, went down in a spiral. Hammer forged barrels were forged around a mandrill, with grooves cut into the mandrill at the required twist or turn and size of the grooves.
Even today hammer-forged barrels are made from a steel billet with a hole through and a mandrill in the size of the bore and grooves for the required caliber. The billet is rotated and while hammers forge the billet until it fits tightly over the mandrill and is then slowly twisted out by the grooves.
Drawn barrels are very smoothly drilled to the bore size of the caliber and a mandrill cut with grooves is then pushed through the barrels pushing the metal between the groove away, leaving the grooves to create the twist in the barrel.
We measure the twist of grooves in the barrel in the number of inches for every complete turn of the groove and vary from about one turn in seven inches to one in sixteen inches. The longer the bullet the more difficult it is to stabilize by turning and therefore would longer bullets have faster turning grooves like one turn in seven or 8 inches. (To explain the principle: -take a kiddies top and make it turn with the twist of the fingers, then take a long pencil with a sharp point and make it turn on the point - it will have to rotate much faster to be able to turn on the point.) The grooves in the barrel make the bullet spin in order to achieve accuracy. The twist of the grooves in the barrel is determined by the length of the bullet and also the velocity at which the bullet is fired. A 223 rifle with a .224 diameter bullet shooting at 3200ft/sec have a twist of 1 turn in 10 inches while a 22-250 shooting the same bullet at a velocity of 3700 ft/sec. has a twist of 1 turn in 14 inches.
We also have another influence in the accuracy of a rifle and that is the shock waves caused by the combustion of the powder. For further information see our section on reloading.
Calibers with larger diameter bullets like the 458 Winchester require fast burning powders and calibers with large cases and smaller diameter bullets like a 264 Winchester need slow burning powders. Fast burning powders reach peak pressures in the chamber much faster than the slow burning powders.
All people who reload their own cases know that with every powder and case lot of powder, a specific charge will have the most accurate result. We have never found a rifle with a good barrel using jacketed bullets that we have not been able to load to achieve a good grouping and therefore believe that every rifle made to the correct specifications should give satisfactory results.
We would also like to say that we have always found Somchem powder very good and people experiencing problems, are using the wrong powder or trying to get groupings with too light a bullet or too high a velocity. We have, however, found that Somchem no longer gives us lot numbers. This does not mean that the burning rate of the next production of powder is the same as the previous lot, it only means that they didn't do the testing. The result being that with every tin of powder, we would have to check the load and the grouping.

LENGTH OF THE BARREL.

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It is normally accepted that a long barrel is more accurate, while the length of the barrel, within limits, does not effect accuracy. If we, for instance, take a R1 rifle, the barrel is short and thin and yet it shoots very well.
We accept that a caliber with fast burning powder can have a shorter barrel than a barrel for a caliber using slow burning powder. All we really need are long enough barrels to be able to utilize the full expanding action of the burning gasses.

It is normally accepted that S335 powder reaches peak pressure by the time the bullet traveled 120 to 150 mm. While S 385 in a 7mm Rem magnum would need a longer distance for complete combustion. (Information by Somchem.)

A 24 inch or 610mm barrel is the normal length used by manufacturers and we use that as the standard for calculating the velocity increase or loss with different barrel lengths.

Ft/sec

26

24

22

20

18

3000

+1.43%

3000

-1.63%

-3.47%

-5.63%

2750

+1.35%

2750

-1.53%

-3.00%

-5.31%

2500

+1.16%

2500

-1.28%

-2.76%

-4.48%

2250

+0.89%

2250

-0.98%

-2.13%

-3.47%

2000

+1.04%

2000

-1.10%

-2.40%

-3.92%

Table 3

As most calibers shoot at too high velocities for the tough SA game it could be an advantage to reduce the velocity by using shorter barrels and have a better balanced rifle at the same time.

EXTERNAL BALLISTICS, THE BULLET IN FLIGHT.

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External ballistics is the most interesting subject any hunter or rifleman can ever study and it will provide many hours of fascination and joy and at the same time will improve shooting results. We are not equipped to do all the testing and calculating ourselves, but rely and get our information from the excellent BALLISTIC COMPUTER PROGRAMS available on the subject.
External ballistics are mainly determined by the velocity of the bullet, the weight and the ballistic co-efficient (BC) (streamlined shape) of the bullet.
When the bullet leaves the muzzle it hits a solid wall of air, the velocity of the bullet makes the air very hard to penetrate. Every bullet starts losing velocity and drop from the trajectory of flight as soon as it leaves the barrel and the bullet drop increases as the velocity of the bullet decreases until, somewhere, the bullet hits the target or falls to the ground. Different calibers have different standard velocities for every bullet weight used, but the maintenance of the velocity and therefore the bullet drop is determined by two factors:

Ballistic coefficient (BC) or the streamline quality of the bullet

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A long sharp pointed bullet will have less resistance while cutting through the air than a round nosed bullet. If the diameter of a round nosed and a pointed bullet is the same, the resistance will also be the same except that the compressed air is spread over a longer distance of the tapered point in the case of the pointed bullet resulting in a reduction in air pressure and therefore a reduction of air resistance
For example if we take two 180gr bullets from a 30-06 both shot at the same velocities and angle, the velocity and bullet drop would be as follows.

Bullet weight

BC

MV

vel @ 500 m

Bullet drop @ 500 m

180gr spitser

0.361

2700

1667

24.44 inches

180gr round nose

0.217

2700

1190

54.52 inches

Table 4

For a further example we take the different bullet weights of the 30-06, all with the same spitser point shot at the standard velocities for the specific weight of the bullet to determine the effect of BC of the bullet

Bullet weight

BC

MV

Velocity at 1000m

Velocity loss

                        

ft/sec

ft/sec

ft/sec

110 grain spitser

0.221

3400

883

2517

150 grain spitser

0.301

2970

998

1972

180 grain spitser

0.361

2700

1049

1651

220 grain spitser

0.442

2400

1104

1296

180 grain round nose

0.217

2700

790

1910

Table 5

With the identical spitser tips of the first four bullets the effect of sectional density (SD) which is the force caused by the weight of the bullet behind the frontal area, makes the bullet maintain its velocity through the air and after it hits the target. The result of the resistance caused by the 180gr round nose bullet during the flight, can clearly be noticed.
The bullet drop of every bullet fired, is therefore directly controlled by the velocity, the weight and the shape of the bullet. For long distance shots it will be better to use heavy spitser bullets at slower velocities, than light RN bullets or semi spitser bullets.

TERMINAL BALLISTICS

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Terminal ballistics is a subject often discussed, but because it is so difficult to assess and measure, very little is known.
It is however worth looking at a few factors effecting terminal ballistics, especially with the hard skin of our tough African game.
People talk about hydrostatic shock, which is even more difficult to explain. All I know is that I have seen animals fall down like a flash and within a couple of seconds, get up and run off. I think that it was a shot badly placed and the impact shocked the animal and as soon as the adrenaline enters the blood the animal gets up and off it goes. Such an animal I believe fell down because of hydrostatic shock. I have never seen an animal die from shock, which is the upsurge of body liquids caused by the impact of the bullet causing a blackout. At the same time have I never seen animals get up after it went down with a good lung shot. A shot that exits the body will bleed much faster and the reduced pressure in the brain will make it fall down never to get up again.
If you want to have a clean kill you will have to penetrate into the vital areas of the animal and I have found few animals going further than 10 to 15 meters after a good lung shot with a bullet traveling right through the animal.

Penetration

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Bullets must be made economical, accurate and to the same weight it must be formed in a press. In order to make the press last, only copper and lead can be used. Copper is forced into a bullet jacket and is then filled with a lead core by using a high-pressure press.
We must accept that copper and lead in the USA is no stronger than in Germany or in South Africa and the quality of a standard bullet is determined by the way the lead is held inside the copper jacket. The problem is that both lead and copper can only withstand the impact up to a certain velocity before breaking up in fragments, which does not penetrate the body and just make a big surface wound.
Tests have shown that bullets hitting the test target at velocities of up to 1800 ft/sec will not break up and lose some of the weight, while bullets traveling at 2800 ft per second hardly ever retains more than 45% of it's original weight. If you shoot a 180grain bullet and loose 55% of the weight, you only have 81grain left to do the work, in which case it might only penetrate the skin and you lose your animal or follow it for a long time.
As velocity is the culprit we can either use hard and expensive bullets or reduce the velocity of the bullet we shoot. Hunters should not worry too much about bullet drop as shown in the following example.
We show the bullet drop with a telescope zeroed at 150 meter for a 30-06 180gr bullet shot at different velocities.

Weight

velocity

50m

75m

100m

125m

150m

180gr

2700

0.68

1.19

1.23

0.8

0

180gr

2400

1.1

1.65

1.68

1.13

0

Table 6

We notice that the difference in height at 100 mm is only .45 of an inch or 11mm and nobody would wound a buck because of 11mm.

Our formula for penetration.

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If a bullet loses 55% at 2800ft/sec and nothing at 1800ft/sec and the velocity of the bullet starting at 2700 is 2433ft/sec at 100m the bullet would retain 67% of the 180gr while the bullet starting at 2400 is only 2150 at 100m the bullet would retain 88% of its weight.

Bullet gr

vel at 100m

energy at 100 m

SD

% retained

Pen/ability

180

2433

2366

x

0.271

x

67%

=

429

180

2051

1848

x

0.271

x

88%

=

440

Table 7

The slow bullet with the 88% retention in weight has a better ability to penetrate than the faster bullet.
In fact, we will now give the average bullet retention at different velocities as found with different calibers and bullet weights for soft point copper jacketed bullets.

1800

ft/sec

100%

1900

ft/sec

95%

2000

ft/sec

90%

2100

ft/sec

85%

2200

ft/sec

80%

2300

ft/sec

75%

2400

ft/sec

70%

2500

ft/sec

65%

2600

ft/sec

60%

2700

ft/sec

55%

2800

ft/sec

50%

Even if you do not agree with the figures, all calibers in the following comparison will be compared in the same way.
The velocity at any given distance will therefore determine the weight the bullet retained to do the work and penetrate the animal, remembering that a bullet that exits causes a lot more bleeding and the animal does not go very far.
Let us look at the ability of all calibers to penetrate and kill by the same formula by comparing the common factor, using PMP ammunition. I arrived at the formula when a Hunters Association asked us to do an article on what is the better caliber for the bush and what is a better caliber for hunting on the plains.
(Please not that faster shooting calibers have better results at longer distances)

CALIBER

Bullet

Distance

Velocity

Energy

Sectional

Weight

Penetration

weight

meter

ft/sec

ft/pd

density

retained

ability

.22 L.R.

40

100

965

83

0.115

100%

9.5

200

828

61

0.115

100%

7.0

300

727

47

0.115

100%

5.4

223 Rem

55

100

2779

394

0.157

51%

76

200

2383

693

0.157

68%

74

300

2021

499

0.157

88%

68

243 Win

100

100

2684

1600

0.242

56%

217

200

2430

1311

0.242

71%

225

300

2189

1064

0.242

81%

208

270 Win

130

100

2702

2107

0.242

55%

280

200

2463

1750

0.242

73%

309

300

2236

1442

0.242

82%

286

150

100

2534

2138

0.279

63%

376

200

2323

1798

0.279

73%

366

300

2122

1500

0.279

84%

352

270 SABI

150

100

2350

1542

0.279

82.5%

355

200

1963

1284

0.279

97.5%

349

300

1785

1061

0.279

100%

296

7 X 57

152

100

2297

1781

0.269

75%

359

200

2108

1500

0.269

85%

384

300

1929

1255

0.269

94%

317

170

100

2248

1907

0.301

78%

448

200

2074

1624

0.301

84%

410

300

1909

1375

0.301

95%

393

7 mm RM

152

100

2798

2641

0.269

50%

355

200

2586

2257

0.269

62%

376

300

2384

1918

0.269

72%

371

170

100

2560

2294

0.301

63%

435

200

2373

2125

0.301

72%

460

300

2194

1817

0.301

80%

437

308 Win

150

100

2798

2187

0.226

62%

306

200

2337

1818

0.226

73%

300

300

2122

1500

0.226

84%

285

180

100

2310

2133

0.271

75%

433

200

2093

1750

0.271

85%

403

300

1887

1423

0.271

95%

366

30 - 06

150

100

2581

2219

0.226

61%

306

200

2354

1846

0.226

72%

300

300

2139

1524

0.226

84%

289

180

100

2391

2285

0.271

70%

433

200

2169

1880

0.271

82%

418

300

1959

1634

0.271

92%

383

220

100

2219

2405

0.331

79%

629

200

2045

2043

0.331

88%

595

300

1880

1727

0.331

96%

549

300 Win M

180

100

2642

2789

0.271

56%

423

200

2407

2316

0.271

70%

439

300

2185

1907

0.271

81%

419

220

100

2435

2896

0.331

68%

652

200

2252

2477

0.331

77%

631

300

2077

2108

0.331

84%

586

303 Brit

150

100

2454

2006

0.222

67%

298

200

2217

1636

0.222

79%

287

300

1992

1322

0.222

90%

264

174

100

2259

1972

0.257

77%

390

200

2068

1653

0.257

87%

370

300

1887

1373

0.257

96%

340

338 SABI

200

100

2414

2587

0.250

70%

452

200

2189

2120

0.250

80%

530

300

1977

1736

0.250

90%

390

250

100

2137

2620

0.313

87%

713

200

2003

2226

0.313

90%

627

300

1842

1882

0.313

96%

566

275

100

2093

2674

0.344

85%

781

200

1942

2302

0.344

92.5%

732

300

1798

1973

0.344

100%

678

300

100

1871

2332

0.375

100%

875

200

1660

1834

0.375

100%

688

300

1469

1437

0.375

100%

539

9.3 X 62

250

100

2166

2603

0.268

82%

572

200

1901

2005

0.268

90%

484

300

1658

1526

0.268

100%

408

286

100

2107

2818

0.307

85%

735

200

1878

2240

0.307

96%

660

300

1667

1764

0.307

100%

542

375 H+H

286

100

2302

3364

0.291

100%

979

200

2001

2542

0.291

100%

739

300

1726

1892

0.291

100%

550

300

100

2266

3421

0.305

77%

803

200

1992

2644

0.305

90%

726

300

1740

2018

0.305

100%

614

458 Win

500

100

1829

3789

0.347

100%

1315

200

1560

2754

0.347

100%

952

300

1330

2004

0.347

100%

695

We may reason that we can use better constructed bullets like Swift A frame, Woodley, Barnes X or GS Bullets, but they are expensive and with some it is often very difficult to get a good grouping.
The Swift A Frame is an outstanding bullet but not easy to find and very expensive. Woodley bullets are also very expensive and do not always perform as would be expected as the lead can sheer out of the jacket. Barnes X and G S are solid copper bullets, which are hard on the barrel, can never be used in a double barrel rifle and are also difficult to group well. G S Bullets have developed low pressure solid bullets for high velocities.
We can use almost any bullet and at the right velocities be very successful especially if we shoot for the vital areas.

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