Bucking wind vrs BC

[onesonek]

I have a couple of friends who shoot long distance matches and they say on a windy day the larger bullets used in larger calibers walk all over their 6mm and 6.5mm cartridges because the bigger caliber bullets have less drift. I have stayed out of this because I have really enjoyed reading this, but the fact is the heavier bigger bullets at very long ranges will have less drift and the evidence from my friends at their matches makes a strong case indeed, especially their ribbons and trophies. Desert Fox is correct in the final analysis.

I shoot matches every month precision f class and tactical matches if your friends are using a higher bc bullet than .612 which is found in a 140vld or a 618 bc in a 140 Berger hybrid they Will drift less assuming there going as fast or faster but to say they walk all over them that's untrue if you ever decide to shoot a match where there is timed strings of 7-10 shots per string of fire at varying distances pay attention to what the top guys are using I would bet there would be one of them using a 260, 6.5-284,6.5x47, or a creedmore.

I haven't shot long range with anything bigger than .30 caliber ( some competition some 30 yrs ago), so I really can't say how I feel about a .338 or in that realm being better or easier to shoot. But it sounds like maybe a confidence thingy in part to me,,still my congratulations on their success's. Then again,,,,
I'm not sure what class, but recall at least one 1000 record being shot with the somewhat dimunitive 6BR just ovet 4". Also,,and again not knowing the class particulars another record, with .50 that was just under 2". I guess those that care, can decide for themselves.
That said, if I got back into competition, I don't know what I would go with. As for now I'm happy just shooting against myself and mother nature, with the XP in the 6mmAI.

 

[SJB358]

Great talk here. Pretty interesting. I am kinda leaning on Jeff and Trevor here. It is all great information though. I guess getting out and shooting is the best way to come up with your own little theories and make it work!

 

[onesonek]

Great talk here. Pretty interesting. I am kinda leaning on Jeff and Trevor here. It is all great information though. I guess getting out and shooting is the best way to come up with your own little theories and make it work!

It really don't matter Scotty whom you lean on really, but I too would trust those whom do long range more regularly than myself. Once one learns the exterior ballistics, (of which I still learn something from other's all the time due not having it quite right due to my faulty intrepretation, or just plain forgetful),,,,,,,,, it boils down to 10% knowledge and 90% skill.

 

[SJB358]

Great talk here. Pretty interesting. I am kinda leaning on Jeff and Trevor here. It is all great information though. I guess getting out and shooting is the best way to come up with your own little theories and make it work!

It really don't matter Scotty whom you lean on really, but I too would trust those whom do long range more regularly than myself. Once one learns the exterior ballistics, (of which I still learn something from other's all the time due not having it quite right due to my faulty intrepretation, or just plain forgetful),,,,,,,,, it boils down to 10% knowledge and 90% skill.

Yup, I didn't mean to discount the rest of you at all in my last statement at all, it is just that you can only account for so many variables you can really control and measure, after that, it comes down to knowing your gear and having confidence in your shooting.

 

[bullet]

Yup, I didn't mean to discount the rest of you at all in my last statement at all, it is just that you can only account for so many variables you can really control and measure, after that, it comes down to knowing your gear and having confidence in your shooting.

Yes!! That is it in a nutshell. :mrgreen:

 

[onesonek]

Great talk here. Pretty interesting. I am kinda leaning on Jeff and Trevor here. It is all great information though. I guess getting out and shooting is the best way to come up with your own little theories and make it work!

It really don't matter Scotty whom you lean on really, but I too would trust those whom do long range more regularly than myself. Once one learns the exterior ballistics, (of which I still learn something from other's all the time due not having it quite right due to my faulty intrepretation, or just plain forgetful),,,,,,,,, it boils down to 10% knowledge and 90% skill.

Yup, I didn't mean to discount the rest of you at all in my last statement at all, it is just that you can only account for so many variables you can really control and measure, after that, it comes down to knowing your gear and having confidence in your shooting.

I know you didn't Scotty,,,,and very true on the rest!

 

[Horsethief]

Confirm this, if you please.
--Ballistic Coefficient is a function of bullet shape (round nose, flat nose, spitzer, boat tail, flat bottom) lenght, and velocity
--Velocity is a function of BC, bullet weight, chamber pressure and barrel length
--Lag time is purely related to velocity

 

[Horsethief]

Lag time is the only thing that affects amount of wind drift. That is the actual flight time to target minus what the flight time would be in a vacuum. Momentum has no effect on this value. BC does. The only reason a slower, heavier bullet can drift less is if it has a significantly higher B.C. The direction of the wind makes no difference in terms of which bullet will fair better.[/quote]

Wind direction makes a large difference in how much a hunter's bullet is moved by the wind. With the same bullets fired with the same load from the same rifle, a pure cross-wind will move the bullet much more L or R than a slightly quartering wind of equal speed.

From 300yds, a 165gn boat tail at nearly max velocity will drift more to the side in a cross-wind than a 180gn bullet (also at nearly max velocity) of the same caliber from the same rifle.

 

[onesonek]

Confirm this, if you please.

I can't say I'm totally correct but my understanding of such

--Ballistic Coefficient is a function of bullet shape (round nose, flat nose, spitzer, boat tail, flat bottom) lenght, and velocity

missing weight to bore ratio


--Velocity is a function of BC, bullet weight, chamber pressure and barrel length

more like velocity is a product of expansion ratio, bullet to charge weight ratio, pressure, and barrel length. Yes on BC, as MV will vary the BC to some degree.


--Lag time is purely related to velocity

lag time is related to drag and rate of deceleration, which have variations due design and current external forces.

 

[ROVERT]

Lag time is the only thing that affects amount of wind drift. That is the actual flight time to target minus what the flight time would be in a vacuum. Momentum has no effect on this value. BC does. The only reason a slower, heavier bullet can drift less is if it has a significantly higher B.C. The direction of the wind makes no difference in terms of which bullet will fair better.[/quote]

Wind direction makes a large difference in how much a hunter's bullet is moved by the wind. With the same bullets fired with the same load from the same rifle, a pure cross-wind will move the bullet much more L or R than a slightly quartering wind of equal speed.

You've taken what I've written out of context. When two bullets are fired under identical atmospheric conditions, the direction of whatever wind is present does not affect one bullet more than the other. When looking at wind, one needs to look at only the vector value that is 90 degrees to the flight path. And yes, Charlie, I am ignoring any vertical wind components here. As far as I can tell those are nearly impossible to judge and compensate for and is also beyond the scope of this thread.

There are other things that dictate exactly where a bullet goes. The Coriolis Effect is one of them. Mass (beyond its role in determining an accurate ballistic coefficient or drag coefficient) is not one of them. That is what this thread is about.

The effect that a cross wind has on a bullet comes down to only lag time. Lag time is not based solely on velocity. It is based on velocity and drag. Specifically it is the amount of time for which drag sets back a bullet and allows a cross wind to act on it.

We can argue about ballistic coefficients all day long and whether or not we should be using G1, G7, a range of G1's at different velocities or some other form of drag coefficient but what it comes down to is how long the bullet is in the air on the way to the target and how long that bullet would have been in the air had the entire flight been in a vacuum.

 

[onesonek]

"Momentum has no effect on this value."
Yes it does,,via the drag coefficient.
At least thats how I understand it.

 

[ROVERT]

Once one learns the exterior ballistics, (of which I still learn something from other's all the time due not having it quite right due to my faulty intrepretation, or just plain forgetful),,,,,,,,, it boils down to 10% knowledge and 90% skill.

I'll agree with that. I'm unfortunately not a long range shooter. I would like to be. It is something that interests me greatly and I have done a fair amount of studying on. I think I have a pretty good grasp on the physics behind much of it. It doesn't matter if someone knows exactly how to calculate these things when they're behind the rifle. They just need to know how their bullets react to what ever conditions present themselves. Understanding the concepts would be useful in determining which bullet to use.

This thread was started by someone postulating that a heavier bullet is somehow better at "bucking the wind" than a lighter bullet based on its advantage of mass. Its mass is not directly relevant, its resistance to drag is.

 

[Horsethief]

How is it that a 165gn bullet with a higher velocity and lower BC than a 180gn bullet is moved more by a cross wind than the 180gn bullet with a lower velocity and a higher BC?

 

[ROVERT]

How is it that a 165gn bullet with a higher velocity and lower BC than a 180gn bullet is moved more by a cross wind than the 180gn bullet with a lower velocity and a higher BC?

Please go read this thread from the beginning. What the heck, I guess I'll say it again... It's the difference in lag time.

 

[ROVERT]

"Momentum has no effect on this value."
Yes it does,,via the drag coefficient.
At least thats how I understand it.

This is a little outside of what is being discussed here, but are you sure? I believe mass comes into play in determining a drag coefficient or ballistic coefficient, but I'm not sure momentum does.

Either way my premise has been that wind deflection is based on ballistic/drag coefficient and muzzle velocity (which determines lag time). I haven't seen anything yet that makes me think otherwise.

 

[onesonek]

How is it that a 165gn bullet with a higher velocity and lower BC than a 180gn bullet is moved more by a cross wind than the 180gn bullet with a lower velocity and a higher BC?

Rate of deceleration is higher for the lower BC.


This thread was started by someone postulating that a heavier bullet is somehow better at "bucking the wind" than a lighter bullet based on its advantage of mass. Its mass is not directly relevant, its resistance to drag is.

But indirectly mass is, as it is part of the formula of Drag. Or another way to think of it,,,mass is to drag, what length is to BC, without adding all the other particulars. Both affect ToF

 

[Horsethief]

Without making any changes to the scope settings, make a 3-shot group with light-for-caliber bullets in a cross wind at a target about 250-300yds away, then do the same with heavier bullets of the same caliber, such as 150gn and 180gn bullets from a .308 Win or 300 magnum. The heavier ones are going to drift less, even though they're in-flight longer, and that makes them more desired.

Hunt where the wind is a factor and there will be two things you likely take away from it. (1) judging the velocity of the wind can be difficult and (2) your compensation with either clicks on the scope/range or hold-off distance L-R was not correct. It's also possible that on a long shot the wind velocity is much higher half-way to the target than it was where you fired the bullet. Even when you do everything right and you're shooting in swirling wind it is a mess, at best.

All this discussion is worthless if you can't get the range and wind right. If you do it right, you'll probably get your game. If you don't get it right, you're making noise with a rifle.

Good luck this season, fellow hunters.

 

[onesonek]

"Momentum has no effect on this value."
Yes it does,,via the drag coefficient.
At least thats how I understand it.

This is a little outside of what is being discussed here,
not really

but are you sure?
pretty much so, but if not, I will stand to be corrected.


I believe mass comes into play in determining a drag coefficient or ballistic coefficient, but I'm not sure momentum does.
where there is mass and motion, there is momentum,,,,, so it's there indirectly as part of the drag equation
(To clairify,,I completely forgot about drag in a previous post. Of which may sound contradicting to this one,,,,just slap me silly )

Either way my premise has been that wind deflection is based on ballistic/drag coefficient and muzzle velocity (which determines lag time). I haven't seen anything yet that makes me think otherwise.

But earlier, the premise was just velocity and BC. Now there is the inclusion of drag. We're on the same book and same page for the most part, just different paragraphs. It seems you are or were looking at the simplfied results, rather than entire physics at play. But again, I could be totally off base in that understanding.

 

[ROVERT]

"Momentum has no effect on this value."
Yes it does,,via the drag coefficient.
At least thats how I understand it.

This is a little outside of what is being discussed here,
not really

but are you sure?
pretty much so, but if not, I will stand to be corrected.


I believe mass comes into play in determining a drag coefficient or ballistic coefficient, but I'm not sure momentum does.
where there is mass and motion, there is momentum,,,,, so it's there indirectly as part of the drag equation
(To clairify,,I completely forgot about drag in a previous post. Of which may sound contradicting to this one,,,,just slap me silly )

Just because momentum is present during a bullets flight does not mean it contributes to the bullet's ballistic coefficient. That's kind of like saying you'll get fat by eating salads at McDonald's because they also serve french fries. Momentum may be a factor in calculating B.C., I'm not sure, but you can't draw connections like that.

Either way my premise has been that wind deflection is based on ballistic/drag coefficient and muzzle velocity (which determines lag time). I haven't seen anything yet that makes me think otherwise.

But earlier, the premise was just velocity and BC. Now there is the inclusion of drag. We're on the same book and same page for the most part, just different paragraphs. It seems you are or were looking at the simplfied results, rather than entire physics at play. But again, I could be totally off base in that understanding.

When you're calculating flight times, you can use a formula that uses a drag coefficient or a ballistic coefficient. I'm not going to declare one more accurate than the other. My premise has not changed. The bullets ability to overcome drag (whether you use drag coefficient or ballistic coefficient) and initial velocity are what determines wind deflection.

 

[ROVERT]

Without making any changes to the scope settings, make a 3-shot group with light-for-caliber bullets in a cross wind at a target about 250-300yds away, then do the same with heavier bullets of the same caliber, such as 150gn and 180gn bullets from a .308 Win or 300 magnum. The heavier ones are going to drift less, even though they're in-flight longer, and that makes them more desired.

The issue is lag time, not total flight time. It's not directly because they have more mass, it is because the bullet with more mass has a shorter lag time due to it being "more slippery".