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Wind Drift

 
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  #36  
Old 06-22-2012, 02:56 PM
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Re: Wind Drift

I like things simple and exaggerated to make the answer more obvious. If i hang a train car from a cable and pretend im the wind and push on it vs hanging a piece of pvc - the lighter pvc is going to push alot farther with the same force than the train car so a lighter bullet (same surface area will move farther) in the same amount of flight time.?? hope that makes sence.

That only addresses part of the question but it takes more to move heavier objects
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  #37  
Old 06-22-2012, 08:47 PM
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Re: Wind Drift

Wildrose, I want to make sure we're on the same page. Two points we disagree on are 1. whether b.c. is more important than form factor ( aka shape), and 2. comparing apples to apples.
1. let's compare two bullets. The hornady 208 amax( great shape), and sierra's 240 gr. SMK. The hornady has a G7 bc of .325, and Bryan Litz tells us the Sierra's is .331. higher b.c.=lessdrift? let's see.
@2500fps the 208 amax has 78.6 inches of drift.
@2500fps the 240 smk has 76.6 inches of drift.
okay so higher b.c. means less drift, until we realize we are pushing the 240 at max pressure and we can still drive the 208 faster. assuming equivalent energy, the 208 can reach 2685fps.
@2685 the 208 has 69.9 inches of drift.
the reason for this is the 208 has a i7 form factor near .96, meaning less drag than the g7 model. The 240 smk has a form factor of 1.092, more drag than the g7 model. The only reason the 240 bc is higher is because it is heavier, but because of shape, it is less ballisticaly efficient. Are you still with me?
......please include the bc's you are entering, sometimes manufacturers are way off. (and that's probably the reason for confusion)
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  #38  
Old 06-23-2012, 12:20 AM
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Re: Wind Drift

Quote:
Originally Posted by ajhardle View Post
Wildrose, I want to make sure we're on the same page. Two points we disagree on are 1. whether b.c. is more important than form factor ( aka shape), and 2. comparing apples to apples.
1. let's compare two bullets. The hornady 208 amax( great shape), and sierra's 240 gr. SMK. The hornady has a G7 bc of .325, and Bryan Litz tells us the Sierra's is .331. higher b.c.=lessdrift? let's see.
@2500fps the 208 amax has 78.6 inches of drift.
@2500fps the 240 smk has 76.6 inches of drift.
okay so higher b.c. means less drift, until we realize we are pushing the 240 at max pressure and we can still drive the 208 faster. assuming equivalent energy, the 208 can reach 2685fps.
@2685 the 208 has 69.9 inches of drift.
the reason for this is the 208 has a i7 form factor near .96, meaning less drag than the g7 model. The 240 smk has a form factor of 1.092, more drag than the g7 model. The only reason the 240 bc is higher is because it is heavier, but because of shape, it is less ballisticaly efficient. Are you still with me?
......please include the bc's you are entering, sometimes manufacturers are way off. (and that's probably the reason for confusion)
We're not comparing apples to apples here since you can't possibly push the 240gr fast enough with a .308 case to take advantage of it's higher BC. Once again if we stick to the realm of reality you'd be lucky to find a load capable of even 2250fps in a .308 with that bullet without dangerous pressure issues developing.

You are getting to the realm of ridiculous when you have to go so far as to use a .308 win pushing a 240gr bullet to make your case.

All of the information I used is included in the ballistic tables at those links I provided.
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  #39  
Old 06-23-2012, 01:44 AM
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Re: Wind Drift

Okay, but my case is not to illistrate what can be done to a .308. I simply am trying to show that shape and velocity are very critical components of wind drift, and that higher b.c. is a great indicator, it can sometimes deceive.
I'm going to use a basic example right from hornady's load manual, under .308 win.
the 190 btsp with a b.c of .491 and the 168 amax witha b.c. of .475.
These are not apples to apples, i will get to that later. these just show how important shape is in the ballisitic coefficient equation. the 190 has a higher bc only because it is heavier. Hornady suggest max vel. for each is 2600 and 2400. Because the 190 is heavier, it leaves the muzzle at a lower speed.
Ballistics Calculator v1.0
Ballistics Calculator v1.0
as you can see, the 168 drifts 106 inches and the 190 drifts 118. The higher bc has more drift in this scenario.
The advantage of the heavy bullet is that it will not lose velocity and eventually the 190 will have less drift. I ran the ballistics on Point Mass Ballistic Solver and the 190 has less wind drift past 2300 yards. I think 2300 yards is past this cartriges functional range, so I would use the 168.
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  #40  
Old 06-23-2012, 02:08 AM
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Re: Wind Drift

Quote:
Originally Posted by ajhardle View Post
Okay, but my case is not to illistrate what can be done to a .308. I simply am trying to show that shape and velocity are very critical components of wind drift, and that higher b.c. is a great indicator, it can sometimes deceive.
I'm going to use a basic example right from hornady's load manual, under .308 win.
the 190 btsp with a b.c of .491 and the 168 amax witha b.c. of .475.
These are not apples to apples, i will get to that later. these just show how important shape is in the ballisitic coefficient equation. the 190 has a higher bc only because it is heavier. Hornady suggest max vel. for each is 2600 and 2400. Because the 190 is heavier, it leaves the muzzle at a lower speed.
Ballistics Calculator v1.0 -
Ballistics Calculator v1.0 -
as you can see, the 168 drifts 106 inches and the 190 drifts 118. The higher bc has more drift in this scenario.
The advantage of the heavy bullet is that it will not lose velocity and eventually the 190 will have less drift. I ran the ballistics on Point Mass Ballistic Solver and the 190 has less wind drift past 2300 yards. I think 2300 yards is past this cartriges functional range, so I would use the 168.
You're still using a bullet so heavy it cannot be launched at a velocity which allows ti's higher BC to be utilized.

Now let's try the same two bullets out of a 300 Rum and see how the equation works out?

168gr Amax-3400fps-

Ballistics Calculator v1.0- WD 2.1

190gr BTSP-3200

Ballistics Calculator v1.0- WD 2.2

208-Amax-3050

Ballistics Calculator v1.0- WD 1.6

You see when we use apples to apples comparisons in cases that can utilize the full potential of the higher BC heavier bullets, the results are significantly different.

Launching a big heavy bullet at low velocities from an overloaded case is not going to give you the same results as using a bullet that's acutally fit for that case which can best maximize the potential of the bullet/case/powder combo.

Remember BC's are not static, they vary as velocity varies
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  #41  
Old 06-23-2012, 09:30 AM
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Re: Wind Drift

No, i've lost you. Let's stay on subject. The .208 has an excellent form factor and lots of weight and is by far the best choice of the three for long range applications. no contest.
That reinforces by point. form wins.
I ran the ballistics on the other two out to 2000 yards. 168@ 3400 has 75" drift and 190 has 77" at 1000yards. Granted these numbers are close enough to ignore in reality, but they are factual.
The 190 does have a higher bc, so eventually it will have less drift, at 1800 yards in this comparison.
So the 190 wins. High bc works better at long range, but i dont think either of these are acceptable for 1800 yards, so the 168 wins in practical app.

Last edited by ajhardle; 06-23-2012 at 12:30 PM.
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  #42  
Old 06-23-2012, 09:37 AM
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Re: Wind Drift

Sorry I missed your comment that b.c.s vary. That just shows what a bad match g1 model is to long range shooting. Sierra's use of banded bc's just confuses people and promotes silly squabbles as this one. We should be using G7 figures. If you don't have access to a more complete list of bc's, all tested the same, and not from manufacturers estimates, guesses or just plain lies, I can suggest where you can get them.
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