The depth of penetration of a bullet is directly proportional to its Sectional Density. However, it is also directly proportional to the force with which the bullet impacts the target (which, for the purposes of this paper, is called Impact Force or IF).

The Impact Force is calculated as follows:

IF = Bullet Weight (pounds) x Velocity (fps)

or

By combining the two factors (multiplying SD by IF), the relative penetration performance of different cartridges may be easily compared (assuming non-expanding bullets for comparison pupposes). As a useful reference, the SDIF Ratio has been tabulated. The SDIF Ratio is the SDIF for the each of the selected cartridges compared to (divided by) the SDIF of the typically "mild-mannered" 100 grain .243 Winchester cartridge.

It is important to note that this approach is also very useful comparing the relative performance of handgun cartridges and just as useful comparing the relative performance of handgun cartridges with rifle cartridges.

Cartridge

Cal.
(in)

SD
(lbs/in²)

BW
(grains)

V @ 100yd
(fps)

IF @ 100yd
(lb�fps)

SDIF @ 100yd
(lbs²�fps/in²)

SDIF
Ratio

.243 Win

0.243

0.242

100

2709

38.7

9.36

1.00

.257 Rob

0.257

0.253

117

2291

38.3

9.69

1.03

.260 Rem

0.264

0.287

140

2554

51.1

14.66

1.57

.270 Win

0.277

0.279

150

2504

53.7

14.99

1.60

7mm Mag

0.284

0.266

150

2927

62.7

16.66

1.78

.30-30

0.308

0.226

150

1973

42.3

9.55

1.02

.308 Win

0.308

0.226

150

2611

56.0

12.64

1.35

.30-06

0.308

0.226

150

2696

57.8

13.05

1.39

.30-30

0.308

0.256

170

1895

46.0

11.78

1.26

7mm Mag

0.284

0.310

175

2645

66.1

20.50

2.19

.308 Win

0.308

0.271

180

2404

61.8

16.76

1.79

.30-06

0.308

0.271

180

2522

64.9

17.58

1.88

.30-06

0.308

0.331

220

2130

66.9

22.18

2.37

.338 Mag

0.338

0.281

225

2582

83.0

23.35

2.49

.45-70

0.458

0.204

300

1497

64.2

13.11

1.40