Educate Me

[strubedog]

AJ, how does one determine damage of a bullet? I know I recall you saying a 150 grain out of a 300 win mag will do more damage then a 180 etc... How does a person determine that?

What is the ballistic coefficient number and what is it used for?

[johnf]

Re: Educate Me

I'll take a stab at this but I'm not AJ for sure. I would bet that bullet weight + velosity togther get you the energy transferred to the target however you also would have to consider that a fair amount of energy would not be transfered to the target in the case of a pass through, so then you would also have to add bullet expansion and weight retention. If the bullet fragments on impact then the impact point would get a lot of damage, but it may be superifical and not be a lethal shot, while a clean passthrough with little or no expantion would trasfer very little energy to the target, causing minimal damage.

So then bullet weight, speed, weight retention and expantion would together determine the damage of the bullet.

This is purly hypothetical and the numbers are just out of my head and it would be a mericle if they are right. Say you shoot a 243 and use three different bullets on three different deer, they are all 100gr and all use the same powder charge. Your first bullet is a fmj it hits the deer passes through without expanding and exits the deer at 3/4 the velosity it entered. So then only 1/4th it's energy is transfered to the deer and very little colateral damage accures. Bullet number 2 is a ballistic tip, it hits the deer and fragments on impact for some reason. This would transfer 100% of the energy in that bullet to the deer but the damage would be localized to the point of impact and the deer runs off with a broken shoulder. Bullet 3 is a softpoint it hits the deer at the same speed as the other two it expands to twice its size and exits the deer at 1/4th the speed that it entered. So then in the process of entering the deer expanding and exiting the deer the bullet trasfered 3/4ths of it's energy to the deer.

So bullet 3 would cause the most damage.

I think......................

[AJ]

Re: Educate Me

John is sort of correct, but I think he got off on a different path. You are referring to energy levels dumped into the target. Its part of the equasion but only 1/3 of it.

How a person tells how much damage will occur is based on a few things like impact velocity, bullet construction, target medium.

1. The higher the velocity at impact, the more damage will occur when the identical bullet is fired at different velocities (or distances). The farther the shot the less velocity at impact.

2. The bullet design or construction will also determine how much damage is going to occur. Like John mentioned above, are the extreme cases. Keeping everything closely related, a Barnes X-Bullet will cause less damage than a Ballistic Tip Hunting bullet, even though they will both do the job. The construction will determine how fast or how much of the bullet will expand. The more violent or sooner the expansion heppens, the more damage will occur.

3. Target medium is what the bullet will encounter in its path through the target. If the bullet just hits hide, muscle, vital organs, muscle and hide as it exits, it will not expand as much as if it hits the scapula or another shoulder bone. When the bullet hits the hard bones, it will expand faster and shatter the bone.

If the bullet has high enough velocity and if it is a good enough design to pass through after hitting a shoulder or other large bone, it will also use bone fragments as projectiles. Pieces of a shattered bone will fan out from the impact point and cause extra damage than just the bullet could.

When you combine all three of these you can see that a hunter shoots hit whitetail deer at 100 yards, with a 30-06 pushing a 150 gr Hornady spire point at 3000 fps, it will cause more physical damage than a 30-06 shooting a 180 gr Hornady spire point only going 2800 fps. There you have the same bullet construction design, same impact spot on target, but the 150 gr has higher velocity to disrupt the bullet sooner and faster, causing a larger wound channel. The higher energy of the 180 gr bullet does not mean anything since both bullets will pass through. Neither will dump all of its energy into the deer. The 180 will travel farther after it exits the deer but who cares at that point?

Nonw if this was for elk sized game where the bullet would not necessarilly exit, the heavier bullet will penetrate deeper causing the best damage. Now, its a penetration vs damge issue.

To answer your other question, ballistic coefficient is the bullets ability to overcome air. The shape of the bullets ogive and base will make it more or less aerodynamic. Since the gasses stop accelerating the bullet once it exits the muzzle, the bullet obviously slows down. Air resistance will cause the bullet to loose this velocity. The more aerodynamic it is the less wind will push it off target, and the less velotity it will drop as it travels downrange. This gives a flatter trajectory, higher downrange velocity, and higher downrange energy.

The BC of a bullet is determined by at least one of these three ways:

1. Calculation of ballistic coefficient from trajectory. This means zeroing at one distance, say 100 yards and using the same aim point shoot another shot at 200 yards. The difference in the point of impact can determine how much drag was induced on the bullet. The guns accuracy can give bogus readings with this method.

2. Calculation of ballistic coefficient from velocity at two points. You have to use a pair of chronographs to measure both speeds on the same shot for this to be accurate. The farther the distance between readings the more accurate the calculation.

3. Calculation of ballistic coefficient from shape.

C = SD/i = w/id2

Where:

C = ballistic coefficient

SD = sectional density

i = form factor

w = weight of bullet, lbs.

d = diameter of the bullet, in.

Coefficient of form, or form factor, is a mathematical number that relates a bullet’s shape, smoothness and shape at the base. The form factor compares the shape of a bullet being tested to the shape of a standard bullet used in a particular ballistic table like the Ingalls table.

The BC of a bullet changes with atmospheric changes. A bullet will not have the same BC throughout its entire flight. As the bullet sheds enough velocity and drops to around the speed of sound, the BC numbers change a lot.

[johnf]

Re: Educate Me

[ QUOTE ]

John is sort of correct

[/ QUOTE ]

yea!! thats more than I expected.

[strubedog]

Re: Educate Me

So for long range shooting where accuracy and flat trajectory are important a lower BC is desired?

[CDubWSR]

Re: Educate Me

The higher the BC the more aerodynamic. Most of your premium hunting bullets with high BC's are about .441 BC and higher up to about .5. Stuff like barnes tripple shocks, nosler acubonds, ballitic tips, swift sorroco's, sierra game kings, and hornady amax's fall into this range. some may be just a little under that .441. Alot of the guys who shoot long range competitions, like 1000 yards and more, have custom made "wildcat" bullets that have BC's of up around .9, but of course they dont make a very good hunting bullet at all b/c they have super thin copper jackets, but are great for punching paper.

[AJ]

Re: Educate Me

[ QUOTE ]

So for long range shooting where accuracy and flat trajectory are important a lower BC is desired?

[/ QUOTE ]

The higher the number the better it is for long range shooting. Each person has a different view of what long range is. It is also determined by the cartridge. For most modern cartridges, long range starts at 300 yards. Match the bullet to the application.

Here is a comparrison of a 300 Win Mag shooting a pair of 180 gr bullets. The first set of data comes from a polymer tipped boat tail bullet fired at 3000 fps. The second set of data is also a 180 gr bullet fired at the same speed but it is a round nosed bullet.

Code:

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Range Path Velocity Energy ToF Windage

yds in fps ft/lbs sec in

.

Muzzle -1.5 3000 3597 0 0

25 -0.4 2951 3481 0.025 0

50 0.5 2903 3367 0.051 0.1

75 1.1 2855 3257 0.077 0.3

100 1.5 2808 3150 0.103 0.6

125 1.5 2761 3046 0.13 0.9

150 1.3 2714 2945 0.158 1.4

175 0.8 2669 2846 0.186 1.9

200 0 2623 2750 0.214 2.5

225 -1.1 2579 2657 0.243 3.1

250 -2.6 2534 2567 0.272 3.9

275 -4.4 2490 2479 0.302 4.8

300 -6.5 2447 2393 0.332 5.7

325 -9 2404 2310 0.363 6.8

350 -11.9 2362 2229 0.395 7.9

375 -15.2 2320 2151 0.427 9.1

400 -18.9 2278 2074 0.46 10.5

425 -23 2237 2000 0.493 11.9

450 -27.5 2197 1928 0.527 13.5

475 -32.5 2156 1858 0.561 15.2

500 -37.9 2116 1790 0.596 16.9

Range Path Velocity Energy ToF Windage

yds in fps ft/lbs sec in

.

Muzzle -1.5 3000 3597 0 0

25 -0.3 2901 3364 0.025 0.1

50 0.7 2804 3143 0.052 0.3

75 1.4 2710 2935 0.079 0.7

100 1.8 2617 2738 0.107 1.3

125 1.9 2527 2552 0.136 2

150 1.6 2438 2376 0.167 2.9

175 1 2352 2211 0.198 4

200 0 2267 2055 0.23 5.4

225 -1.4 2184 1907 0.264 6.9

250 -3.3 2103 1767 0.299 8.6

275 -5.7 2023 1636 0.336 10.7

300 -8.6 1945 1512 0.373 12.9

325 -12.1 1869 1396 0.413 15.4

350 -16.2 1795 1288 0.454 18.2

375 -21 1723 1187 0.496 21.4

400 -26.6 1653 1092 0.541 24.8

425 -32.9 1586 1005 0.587 28.5

450 -40.1 1521 924 0.636 32.6

475 -48.2 1459 850 0.686 37.1

500 -57.3 1399 783 0.739 42

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Notice the time of flight differences due to air resistance. Also notice the windage difference. The energy level drops off significantly at longer range.