Wind Drift

[ajhardle]

okay, your right that a .308 produces more energy than a .243. But your not comparing apples to apples. The .208 gr Amax is a great long range bullet with low bearing surface and a secant nosecone. hornady's 105 gr. is not bad, but look at the shape. long bearing surface, shorter tangent nosecone can't compete. Run it one more time with a berger 105 hybrid. It's closer in form to the 208. Even with the reduced energy, I came up with 68" wind drift. And remember, with the reduced volume in the bore, the .243 will get huge gains from longer barrel and the .308 can gain some extra velocity, but not much.
I'm glad i took the time to check. I would have thought the energy of the .308 would have made it better.

 

[ajhardle]

You can't push the 208gr to 3000fps in a .308 case.

At 2,500 which is possible however.

E-208 Muzzle = 2880 1,000yds 879 WD=75"

Ballistics Calculator v1.0

.243: 105gr-3,100fps
Em-2240, 1,000yds=517 WD=76.7

Ballistics Calculator v1.0

When we stick to the realm of reality once again, same size case, heavier, higher BC bullett wins out again both energy wise, and wind drift wise.



Again, there are limits to how fast you can push any bullet out of any given case.

........ I know what your trying to say, higher b.c. wins, but it's a little misleading. Let's just say "The heaviest bullet for a given caliber wins, if the shape is similar or better." Key word is shape not heaviest. No-one can argue that.

 

[RMulhern]

The Rifleman's Journal: Cartridges: The .308 Heavy Bullet Conundrum

 

[RMulhern]

http://riflemansjournal.blogspot.com/2009/06/long-range-competitor-looks-at-heavy.html

 

[ajhardle]

I have read more than a few post on this fourm as well as others. That imply that by going to a heaver bullet or to a larger caliber that you will get less wind drift.
Am I mistaken I thought that the weight or the caliber of the bullet had nothing to do with wind drift. The only thing that matters is time of flight. Which means that velocity and balistic coefficient, are the main factors effecting wind drift.
example of this is if you have two bullets Shoot at 3000 fps and are traveling in a 90 degree ten mph cross wind. bullet A is .243 cal 80 gr with a BC of .534 and Bullet B is a .243 cal 105 gr with a BC of .534. They will have the same wind drift and the same drop and the same time of flight at any given range.

So if I'm wrong will some one please teach me what is correct.

DR B

This is the origin of this thread. Does going (question #1) to a heavier bullet or (question #2) to a larger caliber decrease wind drift? (Answer#1) A heavier bullet will be advantageous at longer ranges, because of a higher b.c. provided the form factor is the same (form factor=shape). But going to a larger caliber? (Answer#2)No. Not by itself.form You would have to increase powder capacity accordingly............

 

[WildRose]

okay, your right that a .308 produces more energy than a .243. But your not comparing apples to apples. The .208 gr Amax is a great long range bullet with low bearing surface and a secant nosecone. hornady's 105 gr. is not bad, but look at the shape. long bearing surface, shorter tangent nosecone can't compete. Run it one more time with a berger 105 hybrid. It's closer in form to the 208. Even with the reduced energy, I came up with 68" wind drift. And remember, with the reduced volume in the bore, the .243 will get huge gains from longer barrel and the .308 can gain some extra velocity, but not much.
I'm glad i took the time to check. I would have thought the energy of the .308 would have made it better.

Well then once again you get into the problem with a non apples to apples comparison.

We can use the Berger 210g 30 cal hunting VLD to compare to the berger .243 VLD and we'll get similar results to comparing the AMAX's for each.

Again the higher BC bullet wins out because if flies better, and resists wind effects better than the lower BC bullet.

 

[WildRose]

........ I know what your trying to say, higher b.c. wins, but it's a little misleading. Let's just say "The heaviest bullet for a given caliber wins, if the shape is similar or better." Key word is shape not heaviest. No-one can argue that.

The key word is Basllisic Coefficient which is what you were discounting in the two posts I first replied to.

The weight of the projectile is one of the factors in computing BC.

 

[D*N*R*]

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

 

[ajhardle]

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)

 

[WildRose]

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.

 

[ajhardle]

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.

 

[WildRose]

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

 

[ajhardle]

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.

 

[ajhardle]

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.