Value of Sectional Density, Trajectory Chart, Bullet Weight: BCAC3

Value of Sectional Density, Trajectory Chart, Bullet Weight: BCAC3 (Balistics chart and Graph)

 

20130809 Value of Sectional Density, Trajectory Chart, Bullet Weight: BCAC3 (AK 47 Weights and Velocities)

20130809 Value of Sectional Density, Trajectory Chart, Bullet Weight: BCAC3 (AK 47 Weights and Velocities)

 

Today is part 3 of “Ballistics, Cartridge, & Ammunition Components”. I discuss the numeric and qualitative value of sectional density, what a trajectory chart is and what bullet weight is, and how it is measured in grains.

I want to know if everyone likes when I do a series of posts on a subject, or you would prefer that I spend more time all over the map.  Just leave me a comment below if you want to answer.

If you have ever gone to the store and saw that a bullet was 130 grain, 150 grain, or 170 grain, but you didn’t know what that meant, it is the bullet weight.  Grains is a very small measurement of weight.  It is 64.79891 milligrams and equal to .002 troy ounce.  As you can tell, it is a tiny measurement.  Powder, or charge, can be measured in grain, meaning a single grain of powder, but bullet weight is measured in the grain as a weight measurement.  This is what you may see on a box of ammunition.  The bigger the number, the heavier the box.

A heavier bullet has a couple advantages and drawbacks.  If a heavier bullet is fired at the same speed, it will have a greater impact.  The equation is Force=Mass x Acceleration.  A higher mass with a measured weight of higher grains will have more force on contact than a smaller bullet.  But to get the same speed, you will typically need more charge and a higher pressure.

Weight plays into sectional density, as does the diameter.  You are basically calculating the weight per sectional area of the bullet.  What does this really amount to for a hunter, penetration.  Sectional density is all about how much penetration can you achieve with a bullet.  The equation for sectional density is (Bullet Weight in Grains) / [7000 x (Bullet Diameter in Inches) x (Bullet Diameter in Inches)].

As bullet caliber (diameter) goes up, so must weight so you can get the same depth of penetration because it changes the area in front of the bullet giving more surface area, thereby more resistance.  Usually we use higher caliber bullets for larger game, and we also need penetration depth to go up so it can reach the vital organs.  What this means is that the bullet weight will need to go up substantially which means more of a charge needed.  Ammo manufacturers typically keep the sectional density about the same for particular animals through different bullet calibers allowing an informed hunter to better select the ammunition.  The chart below shows ammunition based on sectional density.

A sectional density of .180 is good for hunting varmints. One of .230 would be good for hunting CXP2 game such as deer.  A SD of .280 would be appropriate for hunting CXP3 game such as elk. And, a bullet with an extreme SD of .330 would be chosen for heavy, thick skinned CXP4 game such like rhinos or elephants.

Caliber

Sectional Density

Frontal Area (in^2)

% Change of Frontal Area

Weight
(grains)

% Change of Weight

             

0.243

0.180

0.046

74

0.257

0.180

0.052

11.85%

83

11.85%

0.264

0.180

0.055

5.52%

88

5.52%

0.277

0.180

0.060

10.09%

97

10.09%

0.284

0.180

0.063

5.12%

102

5.12%

0.308

0.180

0.075

17.62%

120

17.62%

0.323

0.180

0.082

9.98%

131

9.98%

0.338

0.180

0.090

9.50%

144

9.50%

0.348

0.180

0.095

6.00%

153

6.00%

0.358

0.180

0.101

5.83%

161

5.83%

0.366

0.180

0.105

4.52%

169

4.52%

0.375

0.180

0.110

4.98%

177

4.98%

0.416

0.180

0.136

23.06%

218

23.06%

0.458

0.180

0.165

21.21%

264

21.21%

             
             

0.243

0.230

0.046

95

0.257

0.230

0.052

11.85%

106

11.85%

0.264

0.230

0.055

5.52%

112

5.52%

0.277

0.230

0.060

10.09%

124

10.09%

0.284

0.230

0.063

5.12%

130

5.12%

0.308

0.230

0.075

17.62%

153

17.62%

0.323

0.230

0.082

9.98%

168

9.98%

0.338

0.230

0.090

9.50%

184

9.50%

0.348

0.230

0.095

6.00%

195

6.00%

0.358

0.230

0.101

5.83%

206

5.83%

0.366

0.230

0.105

4.52%

216

4.52%

0.375

0.230

0.110

4.98%

226

4.98%

0.416

0.230

0.136

23.06%

279

23.06%

0.458

0.230

0.165

21.21%

338

21.21%

             
             

0.243

0.280

0.046

116

0.257

0.280

0.052

11.85%

129

11.85%

0.264

0.280

0.055

5.52%

137

5.52%

0.277

0.280

0.060

10.09%

150

10.09%

0.284

0.280

0.063

5.12%

158

5.12%

0.308

0.280

0.075

17.62%

186

17.62%

0.323

0.280

0.082

9.98%

204

9.98%

0.338

0.280

0.090

9.50%

224

9.50%

0.348

0.280

0.095

6.00%

237

6.00%

0.358

0.280

0.101

5.83%

251

5.83%

0.366

0.280

0.105

4.52%

263

4.52%

0.375

0.280

0.110

4.98%

276

4.98%

0.416

0.280

0.136

23.06%

339

23.06%

0.458

0.280

0.165

21.21%

411

21.21%

             
             

0.243

0.330

0.046

136

0.257

0.330

0.052

11.85%

153

11.85%

0.264

0.330

0.055

5.52%

161

5.52%

0.277

0.330

0.060

10.09%

177

10.09%

0.284

0.330

0.063

5.12%

186

5.12%

0.308

0.330

0.075

17.62%

219

17.62%

0.323

0.330

0.082

9.98%

241

9.98%

0.338

0.330

0.090

9.50%

264

9.50%

0.348

0.330

0.095

6.00%

280

6.00%

0.358

0.330

0.101

5.83%

296

5.83%

0.366

0.330

0.105

4.52%

309

4.52%

0.375

0.330

0.110

4.98%

325

4.98%

0.416

0.330

0.136

23.06%

400

23.06%

0.458

0.330

0.165

21.21%

485

21.21%

 

Although I already stated this, the idea of sectional density is to calculate the penetration through the animal to reach vital organs, but no further.  This maximizes bullet damage, unless you want to hydro-shock the animal (which I am NOT getting into today).

Something that is related to weight, not density so much is the ballistics trajectory chart or graph.  I don’t want to teach you everything there is to know about a balistics graph or chart, but just a little information to debunk anything that may be erroneous.

Value of Sectional Density, Trajectory Chart, Bullet Weight: BCAC3 (Balistics chart and Graph)

Value of Sectional Density, Trajectory Chart, Bullet Weight: BCAC3 (Balistics chart and Graph)

First, if you look at the chart above, you will se the bullet rises.  So it is a common misconception that bullets always rise first.  WRONG!  Simple physics tells you that the bullets do not rise in and of themselves.  They start of 100% straight with the bore line of the rifle.  The 0 line in the graph above is eye level.  So this firearm is sited in at 50 yards.  Sited this way, the bore angle changes, you are actually pointing the gun upward a little with respect to your eye’s straight line view.

You can see that the standard round drops substantually around 75 yards.  A guy I know, and a reader of the blog, has told me that he actually sites his stuff in at around (i think) 70-75 yards.  He does this because most site at 100 yards and there is already significant drop of the bullet there, meaning lost velocity.  He has a good point, but only if you know the penetration you want and the velocity required for that. 

A nice little rule of thumb that I never knew:  A standard velocity round 0 level will almost not change from 50 feet to 50 yards since the bullet is crossing line of sight on the way up at 50 ft and crossing on the way down at 50 yards.

I hope this has been informative for you!

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