Bucking wind vrs BC

[onesonek]

Momentum doesn't contribute to BC, it does to the Drag Factor by way of mass and velocity, as stated earlier.
Everything works together, not independently. Drag factor, BC, and throw in the gyro factor ect.. Programs that do not make the necessary correction will do at shorter ranges for an estimate. Opinions will vary at what range, one needs to be concern with everything involved. The better programs are still only a guide, for the most part.

If every thing is constant, it would be different story as to your premise. But the only thing that is really finite,,is the bullet is going to hit the ground at sometime!
External factors can change from intital velocity parmeters, which in turn change flight characteristics, even if lag time is or is not affected by only a fraction..... Then think of MV standard deviations. At extreme range, even a low double digit SD can raise heck with your group.
It's not only reading the conditions at the muzzle,,,with wind being the worst for not being constant, you can have all the factors Charlie and DF mentioned. Again, very little if anything is constant with the numbers in flight. The starting numbers initially are only a guide, not an absolute.
Again, at modest ranges the fine points are mute for the most part. However,, when one understands and takes all that knowledge, apply sound shooting fundemntals, and acquiring the skill level,,,long range shooting becomes more an art than a science. But all the science of physics pertaining to ballistics apply,,,not just two. The two will work for an estimate at shorter range's, but true firing solutions have all the factors involved.


That's my take on it, even if my technical is off abit.

 

[ROVERT]

Yes, B.C. values are not constants throughout the range of velocities that a bullet encounters on its way to a long range target. This can have an effect on lag time. This is far beyond the scope of the question asked in this thread. The question was asked if B.C. is the sole contributing factor to "bucking the wind" or if mass also impacts it. The answer is that B.C. and muzzle velocity are the sole contributing factors because they are what dictate lag time.

There are, indeed, a whole host of other factors that determine where the bullet strikes at a given range, but the only thing that affects wind deflection is lag time. If the B.C. (or range of B.C.'s, ie. Sierra) are not accurate, whatever ballistic software you are using will not accurately calculated ToF. If you have a ballistic coefficient(s) that is(are) accurate, you will be able to accurately calculate lag time and therefore wind drift. If you take two bullets of different mass with accurate, equal B.C.'s and fire them at the same muzzle velocity, the bullet with more mass will not be affected less by the wind.

 

[JD338]

Although TOF and BC are the main factors in cutting wind deflection - Momentum, bullet density, bullet velocity and drag is also a contributing factor.

Linear Momentum which is the product of weight times velocity tends to keep the bullet straight. The heavier the bullet, the harder it is for the wind to push it away from it's intended path.

Density- a heavier bullet tends to be denser than the lighter bullet therefore will be influenced less by wind

Velocity and Drag- In order to equal the momentum of the heavier bullet, a lighter bullet has to be push to a higher velocity but, we all know that the lighter bullet will not be able to hold it's velocity at longer distance due to increase drag therefore can be deflected more by the wind.

Bryan Litz in his bullet comparison, as shown in the link provided by Rovert, explained it correctly. To match wind deflection, a lighter bullet has to be pushed to higher velocity when compared to a heavier and bigger caliber bullet. Not sure why Bryan did not include the distance and the tof in his example but I'm pretty sure the 90 grain 223 got to the target sooner than the 220 grain 308. Extend that range further and the 223 bullet will surely be deflected more by the wind than the 308 bullet.

You have to consider the whole flight regime of the bullet when determining how will it behave when subjected to wind. There's no commercial ballistic program out there in the market that can predict with certainty, the effect of wind on bullet. It's all approximation, so you can't rely on them. Empirical measurement and keen observation is much more reliable.

My last 1000 yards score with my 338 Lapua Ackley, shooting the 300 grain SMK, is a good example of why a heavy bullet, at moderate velocity, will fair better on a windy day against faster but lighter bullet.
I find it easy to placed 13 of the 25 bullet into the X-ring. As you can see on the score of shooters, the 338 and the 50's dominated the smaller caliber.

DF,

Your post sums it up well. The larger 338 cals did do well in that match. Those long 300 gr SMK's at 2600-2800 fps are a force to reckon with. Nice shooting BTW!

JD338

 

[Desert Fox]

Allow me to quote Robert A. Rinker wrote in the foreword of his book, Understanding Ballistics.

"As an Engineer, I have found ballistic to be a very frustrating area of Science. There are so many variables that is almost impossible to use formulas that are base on known laws of physics WITHOUT INCLUDING INFORMATION BASE ON ACTUAL TEST. IT IS DIFFICULT TO MAKE POSITIVE STATEMENT THAT ARE NOT BACK UP BY SOME FORM OF TESTING."

ROVERT,
You made this whole business of wind deflection sound so straight forward and simple, relying so much on mathematical formulas as if it is written in stone. You said it yourself that you haven't done any long-range competition or shooting.

When you finally get a chance to do it in the future, please don't forget to tell us your experience.

 

[Oldtrader3]

Colonel Townsend Whelen also said the same thing way back before computers. The theoretical is nice for brain exercise but you have to shoot the course to verify empirical with actual. This is universally true with all empirical engineering calculations.

 

[Desert Fox]

"like the Patagonia Coldbore 1.0"
Without researching it myself further,,,how does one compare to RSI Shooting Lab

Dave,

I'm not familiar with RSI so I can't make comparison. Another Ballistic software that is similar to Patagonia is Lex Talus Corporation Field Firing Solutions. Both are base on Dr. Arthur Pejsa analytic close form solution model. Both of this software is very similar from what I learned and capable of predicting with great accuracy all bullet flight regimes from Supersonic to transonic and even subsonic region. FFS is twice the price of Patagonia. If you are a member at Longrange Hunting, you can buy the Patagonia there at a discount.

I'm currently using Ballistic FTE in my I-Phone. It's a very accurate in predicting trajectory up to 1k. Beyond that however, The prediction is not reliable. So time to upgrade.

 

[onesonek]

Thanks,,,after I asked, I wondered about the odds of you knowing. However, I did glance briefly at their site. It does look to have a few more assets.

 

[ROVERT]

Allow me to quote Robert A. Rinker wrote in the foreword of his book, Understanding Ballistics.

"As an Engineer, I have found ballistic to be a very frustrating area of Science. There are so many variables that is almost impossible to use formulas that are base on known laws of physics WITHOUT INCLUDING INFORMATION BASE ON ACTUAL TEST. IT IS DIFFICULT TO MAKE POSITIVE STATEMENT THAT ARE NOT BACK UP BY SOME FORM OF TESTING."

ROVERT,
You made this whole business of wind deflection sound so straight forward and simple, relying so much on mathematical formulas as if it is written in stone. You said it yourself that you haven't done any long-range competition or shooting.

When you finally get a chance to do it in the future, please don't forget to tell us your experience.

I respect your accomplishments in long range shooting. I know there are other variables in determining your windage. Charlie pointed out a few that are not based on wind. The impact that wind has is very straight forward given a constant wind. It is based on lag time. I understand that in the real world you are very unlikely to have a constant and that reading the wind is very much as much art as science.

This thread asked a pretty basic question. There is a simple answer, a heavier bullet does not resist wind deflection better than a lighter bullet. The bullet that is more slippery does. After a bullet has been given the optimum meplat, ogive and boat tail, the easiest way to make it more slippery is to add length to the bullet. This in turn adds mass. This is why heavier bullets tend to have higher ballistic coefficients. Bullets with equal "slipperiness" fired at the same muzzle velocity will react the same to the wind regardless of their respective masses.

I understand that this stuff is does not, on its own, compensate for real world conditions, but it does explain why some bullets and calibers perform better than others.

Here's something I'd be interested to know. I imagine you have been able to find a ballistic coefficent value that very closely matches the drop of your .338 out to 1000 yds. When you use that B.C., does it not also very closely match wind deflection?

I'm really not trying to be a smart a$$ with all of this. I'm just trying to explain the answer to the original question. When comparing the effects of the wind on two different bullets, lag time is what you need to compare. In the real world it may be difficult to come up with exact numbers, but ballistics software is going to do a decent job of telling you which bullet will fare better, even if the numbers are off a bit.

 

[Guy Miner]

"When you use that B.C., does it not also very closely match wind deflection?"

Very difficult question for me, because wind is so seldom constant. Measured wind at the firing line may not even come close to resembling wind halfway to the target, wind at the highest point of the bullet's arcing trajectory or wind at the target. Not all ranges have good wind flags - my club's 600 yard course is notorious for shifting, hard to detect winds. At my club, I had 168 gr .30 cal bullets blown 18" off course, at 600 yards, by a wind that I could barely see or feel, yet it was moving pretty good out there downrange.

This is why I go back to saying that elevation is easy, and wind is the problem with long range shooting. It's shifting, inconsistent, tough to predict, has abrupt let-offs, and has varying effects on the bullet depending on which direction is strikes the bullet from. Wind can also have a vertical component, not just sideways...

So, I see wind reading as more of an art than a science. It's really hard to KNOW with certainty what the wind is doing, and what it will do to the bullet. All I really can do is do my best with the wind reading, and shoot a bullet that will slice through it relatively well, no matter what it's doing.

Regards, Guy

 

[ROVERT]

"When you use that B.C., does it not also very closely match wind deflection?"

Very difficult question for me, because wind is so seldom constant. Measured wind at the firing line may not even come close to resembling wind halfway to the target, wind at the highest point of the bullet's arcing trajectory or wind at the target. Not all ranges have good wind flags - my club's 600 yard course is notorious for shifting, hard to detect winds. At my club, I had 168 gr .30 cal bullets blown 18" off course, at 600 yards, by a wind that I could barely see or feel, yet it was moving pretty good out there downrange.

This is why I go back to saying that elevation is easy, and wind is the problem with long range shooting. It's shifting, inconsistent, tough to predict, has abrupt let-offs, and has varying effects on the bullet depending on which direction is strikes the bullet from. Wind can also have a vertical component, not just sideways...

So, I see wind reading as more of an art than a science. It's really hard to KNOW with certainty what the wind is doing, and what it will do to the bullet. All I really can do is do my best with the wind reading, and shoot a bullet that will slice through it relatively well, no matter what it's doing.

Regards, Guy

All of that makes sense to me, Guy. I never meant to imply that you could just pull a number off the table for a constant wind, dial it into your scope and have the bullets hit the x ring.

I am standing firm that lag time is what determines wind drift. The shorter the lag time, the less the bullet is affected by whatever wind is present. There are two ways to reduce lag time - increased muzzle velocity and higher ballistic coefficient (or whatever term you want to use to describe a bullet's slipperiness). A bullet with more mass does not have additional ability to buck the wind unless it also has a higher B.C. than the bullet is is being compared to.

 

[mcseal2]

It's a real eye opener to practice in windy conditions for those of you who haven't. I put my gong in a windy divide between two big hills where I get crazy winds nearly every time I shoot. All the posts have been correct so far, but in the real world I feel the best answer is to look for both velocity and BC for windy day shooting at hunting ranges. My max range I'd feel comfortable at in the field is 500yds under very good conditions, although I practice at 600 quite a bit. 500yds is still in the area where velocity (time of flight) and BC are both very important, the high BC hasn't quite taken over yet. I carry a wind meter hunting and have a MOA reticle in my scope and an MOA wind drift chart I carry with me also. The windy area I live in makes me choose rounds that are real efficient out to my 500yd limit, so I end up going with a velocity of 3000fps+ and a BC of .500 or darn close to it for my hunting. If I can get more of either without sacrificing to much of one, I really like that also.

 

[Desert Fox]

the easiest way to make it more slippery is to add length to the bullet. This in turn adds mass. This is why heavier bullets tend to have higher ballistic coefficients.

Go back and research this more and get back to me.

Here's something I'd be interested to know. I imagine you have been able to find a ballistic coefficent value that very closely matches the drop of your .338 out to 1000 yds. When you use that B.C., does it not also very closely match wind deflection?

As a matter of fact I do.

If you go back and look at the score that I posted in my previous post, there's a guy there by the name of Chris shooting a 7WSM. He gave me the recipe from his 7WSM 180 grain Berger load and I have the data for it. He place 17th that day.

Here's the comparison. I think the BC of this two sample bullet is much more closer in real world shooting.

300 SMK - MV 2850 ft/sec, BC- .768
Drop in MOA from my 100 meter Zero - 24.10
TOF to 1K - 1.32 sec
Remaining velocity - 1817 ft/sec

180 grain Berger VLD - MV 3000 ft/sec, BC-.674
Drop in MOA from my 100 meter zero - 22.87
TOF to 1K - 1.30 sec
Remaining velocity - 1754 ft/sec

Here's the interesting part. According to Ballistic FTE, the 180 Berger will have a deflection of 32.61" when subjected to 5 MPH wind full value, whereas the 300 grain SMK will have 34.10".

As you can see the 180 grain Berger has a slight advantage on wind deflection over the 300 SMK even though it has a bit lower BC. The TOF of the 180 is shorter by .02 sec also. This support Bryan Litz contention that a smaller bullet has to be push faster to match the performance of the heavier bullet. So if that's the case, why is it that the 7WSM took a beating from those large caliber heavy bullet. Chris have been shooting long-range match longer than I do and his equipment is top notch.

I guess it's still boiled down to the nut behind the trigger.

 

[Horsethief]

My hunting buddy and I did some bullet vs wind testing a few weeks ago in a 20-25mph cross wind and had nearly the same results @ 300yds. The cross wind pushed the bullets 6-7" to right. Sometimes the wind let down and that messed the hold-off amount. Nothing beats practice in the same conditions you're going to face during hunting season.

Long ago when shooting on 600yd ranges we had large red flags every 200yds. The flag at the target wasn't as important as the flag at the firing line and the flags along the way to the target. By the time the bullet made it 600yds, it had already done all its moving around. Flags along the way were the ones to pay attention to since they indicated the cross-wind or lack thereof. We were using 168gn match bullets with muzzle velocities at about 2650fps.

 

[ROVERT]

As a matter of fact I do.

If you go back and look at the score that I posted in my previous post, there's a guy there by the name of Chris shooting a 7WSM. He gave me the recipe from his 7WSM 180 grain Berger load and I have the data for it. He place 17th that day.

Here's the comparison. I think the BC of this two sample bullet is much more closer in real world shooting.

300 SMK - MV 2850 ft/sec, BC- .768
Drop in MOA from my 100 meter Zero - 24.10
TOF to 1K - 1.32 sec
Remaining velocity - 1817 ft/sec

180 grain Berger VLD - MV 3000 ft/sec, BC-.674
Drop in MOA from my 100 meter zero - 22.87
TOF to 1K - 1.30 sec
Remaining velocity - 1754 ft/sec

Ok, from these number you can calculate lag time. The 180 Berger's lag time is .30 seconds. The 300 SMK's lag time is .27 seconds. Therefore, the SMK should drift less.


Here's the interesting part. According to Ballistic FTE, the 180 Berger will have a deflection of 32.61" when subjected to 5 MPH wind full value, whereas the 300 grain SMK will have 34.10".

Something doesn't make sense with those numbers. When you run the numbers through JBM using Litz's B.C. numbers, you get a 2" less drift with the SMK, not the Berger. When I do the calculations using lag time (based on the ToF and MV you provided) and wind speed I also show an advantage with the SMK (~2.5"). The difference from my calculations and what JBM calculated based on Litz's numbers can likely be attributed to the use of different B.C. numbers (I believe you used G1 to calculate your ToF). Either way the advantage should go to the SMK, not the Berger.

As you can see the 180 grain Berger has a slight advantage on wind deflection over the 300 SMK even though it has a bit lower BC.

The numbers produced by JBM software and by my own lag time calculations do not show that the Berger will have an advantage.

The TOF of the 180 is shorter by .02 sec also.

You can't get hung up on ToF alone unless you have equal muzzle velocities. You need to look at the lag time.

This support Bryan Litz contention that a smaller bullet has to be push faster to match the performance of the heavier bullet.

I believe Litz's contention is that a bullet with a lower B.C. has to be pushed faster to match the performance of a bullet with a higher B.C. Yes it is true that heavier bullets tend to have higher B.C.'s, but they don't always depending on shape, caliber, length, etc. The B.C. is what matters here.

So if that's the case, why is it that the 7WSM took a beating from those large caliber heavy bullet. Chris have been shooting long-range match longer than I do and his equipment is top notch.

I'd postulate that, given equal skill among the shooters, the 7 WSM took a beating because it's lag time was greater and was therefore more affected by the wind.

I guess it's still boiled down to the nut behind the trigger.

Yep, it does. A little advantage in lag time helps, though.

Thank you for playing along here. I know this is probably frustrating you as much as it is me. We might even get to the bottom of this, given enough time.

 

[ROVERT]

the easiest way to make it more slippery is to add length to the bullet. This in turn adds mass. This is why heavier bullets tend to have higher ballistic coefficients.

Go back and research this more and get back to me.

Mass is on the top of the formula for ballistic coefficient. Diameter squared is on the bottom of the formula. If you add mass to bullet proportionately, keeping the same form/shape and just scaling it up, it will raise the B.C., but not by as much as if you had only increased the length to add the mass.

 

[Desert Fox]

So what you're saying is ballistic FTE sucks! That I agree shooting beyond 1000 yard. The trajectory table however was verified in the field with both my 338 and 7 WSM, as long as I keep the absolute pressure out of the equation, it's fairly close, no more than .25 MOA at 1k. The only thing was not verified here is the wind since I cant tell mother nature to keep the speed constant while I'm shooting, and the TOF because I have no access to Doppler radar. We can play the number all day long, but my experienced in the field tells me otherwise.

 

[ROVERT]

So what you're saying is ballistic FTE sucks! That I agree shooting beyond 1000 yard. The trajectory table however was verified in the field with both my 338 and 7 WSM, as long as I keep the absolute pressure out of the equation, it's fairly close, no more than .25 MOA at 1k. The only thing was not verified here is the wind since I cant tell mother nature to keep the speed constant while I'm shooting, and the TOF because I have no access to Doppler radar. We can play the number all day long, but my experienced in the field tells me otherwise.

I can understand that the drop is accurate. Gravity affects a bullet for the entire ToF. The SMK has a longer total flight time and is therefore subjected to the forces of gravity for a greater period of time than the Berger.

I think there is something askew with the wind deflection numbers, though. Unfortunately, it is doubtful that you will ever get mother nature to provide you with a nice constant wind.

Your experience is that the 300 gr. SMK @ 2850 fps is less susceptible to wind deflection than the 180 gr. Berger at 3000 fps. This is fully supported by the fact that lag time is the determining factor in wind deflection.

I'm not trying to say that there is a simple way to determine your windage correction because I doubt there has ever been such a thing as a constant 10 mph wind in a real life shooting situation. As Charlie pointed out, there are factors other than wind that also contribute to necessary windage correction. The key to determining if one bullet/velocity combination is more susceptible to the wind than another bullet/velocity combination really is the lag time.

 

[Desert Fox]

How does adding length make the bullet more slippery!

 

[ROVERT]

P.S. I still had the JBM screen up from running the 300 SMK numbers (using Litz BC). The drop providing by JBM was 25.1 MOA for your load at 1k. That is in the ball park of what you report from FTE/actual findings. I think something is just messed up with the wind numbers.

 

[usmc 89]

Changing the profile of a bullet Will alter bc, length is a byproduct of doing so.