Wind drift relative to bullet weight

[Raythemanroe]

Wind drift relative to bullet weight:

Does a bullet with the same BC but lighter weight have more drift then a heavier bullet with the same BC? Example would be 6mm 115g Berger VLD vs .308 190g SMK.

 

[ShootDots]

I am going to stick my neck out here and give you my 2cents worth. I KNOW it will bring criticism>>>but that's ok. If you have 2 bullets of the SAME B.C. and going at the SAME velocity, it is MY OPINION that the heavier will generally drift in the wind less. I know that the "B.C. Calculators" are to take weight in their theorem. They may in fact do exactly that, BUT I still see, from experience, that heavier bullets drift less. I have also come to a conclusion, based on experience, that there should be TWO (2) B.C.'c, one for trajectory and one for wind drift. Now, let the fireworks begin!

 

[ShootDots]

Oh I understand Donovan... I KNOW I am "mathematically wrong", but my experience tells me differently... it also could be "shooter error" on my part, as the "drift" is not excessive>>>But I notice it.

 

[ShootDots]

I don't believe it is a whole heck of a lot of drift either... Like I said, the difference is small enough that I would NOT absolutely rule out shooter error on MY part! LOL!!!

 

[savagedasher]

I have two dashers one a 7.5 T the other a 8 T Shooting 105 Hybrid the 8 T shoots 3105 The 7.5 Shoots 3072. I get 6'' less drift at 1000yd in the wind with the 7.5 . Two of shooting at the same time along with changing guns. The real kicker is that the 8 shoots better in calm wind. Larry

 

[Raythemanroe]

The same weight and BC bullet can have a higher BC if stabilized better I would think, What I wonder is as a bullet slows at distance wouldn't the heavier retain it's speed and be effected by wind less?

 

[johara1]

When i slowed the Dasher down with the 103 Spencers they were a lot better in the wind ,why i don't have a clue. The 105 Berger hybrid has more vertical than the 115 DTAC. in a head or tail wind, Why i don't have a clue on that one either. The Spencer 103 is better than both of them and going slower,go figure……… That is what i found out,but i'm getting old …..LOL…. jim

 

[savagedasher]

When i slowed the Dasher down with the 103 Spencers they were a lot better in the wind ,why i don't have a clue. The 105 Berger hybrid has more vertical than the 115 DTAC. in a head or tail wind, Why i don't have a clue on that one either. The Spencer 103 is better than both of them and going slower,go figure……… That is what i found out,but i'm getting old …..LOL…. jim

WE both mite be getting too old. I took my 15 year old Grand Daughter who had never shot anything but a 223 at 100 YD. Let her shoot 1000yd with my dasher. With two bad trigger pulls. Her 10 shot group was 7.7 inches. I assume from the target she her bad trigger pull added 2 1/2 ''. So age must be a factor. Larry

 

[Raythemanroe]

When i slowed the Dasher down with the 103 Spencers they were a lot better in the wind ,why i don't have a clue. The 105 Berger hybrid has more vertical than the 115 DTAC. in a head or tail wind, Why i don't have a clue on that one either. The Spencer 103 is better than both of them and going slower,go figure……… That is what i found out,but i'm getting old …..LOL…. jim

Wouldn't the explanation be that the Spencer's are stabilizing better and getting a real world BC that is better? Just like when some one thinks there barrel is a hummer and it bucks the wind better? In reality there both just more accurate so it appears there better.

 

[udiablo]

Are any of you going to the trouble of setting up another chronograph out there to determine what your actual velocity is at the target?

Or are you just working from someone's BC chart?

Now let the flaming begin........

 

[savagedasher]

Are any of you going to the trouble of setting up another chronograph out there to determine what your actual velocity is at the target?

Or are you just working from someone's BC chart?

Now let the flaming begin........

I have only one but I could use yours at 1000 yd. How does that sound. That should start the flame. Larry

 

[22BRGUY]

Does the term "sectional density" have any bearing on this discussion? Just asking......Good post guys.

 

[Raythemanroe]

One chrono for me

 

[bdale]

Does the term "sectional density" have any bearing on this discussion? Just asking......Good post guys.

The sectional density of a projectile can be employed in two area of ballistics. Within external ballistics, when the sectional density of a projectile is divided by its form factor[disambiguation needed] it yields the projectile's ballistic coefficient

Within terminal ballistics, the sectional density of a projectile is one of the determining factors for projectile penetration. The interaction between projectile (fragments) and target media is however a complex subject. A study regarding hunting bullets shows that besides sectional density several other parameters determine bullet penetration.

Only if all other factors are equal, the projectile with the greatest amount of sectional density will penetrate the deepest.

 

[mysticplayer]

Wind drift relative to bullet weight:

Does a bullet with the same BC but lighter weight have more drift then a heavier bullet with the same BC? Example would be 6mm 115g Berger VLD vs .308 190g SMK.

Assuming steady state air, NO but that is not the real world.

what ballistics calculators do not account for well is INERTIA... and that saves your butt on ranges where there is lots of localised turbulence.

No, I am not some math genius but I have seen the effect in LR shooting.

Think driving down the highway in a small car vs a big car. Then you get hit by a gust of wind from a passing semi trailer.

which vehicle gets buffeted more? Small car

So is the same with bullets of varying weights.

My real world experience was shooting a 223/90gr combo vs a 308/200gr combo over two years in Raton, NM. Very bumpy air, twitchy, lots of localised gusts.

The 223/90 was a royal PITA to drive as it was bounced around all over the place when got caught in a gust. The 308 heavies got bounced too but didn't move as far.

Saw that on the same relay with one shooter using a 155.5gr load and a superb wind reader. Gust would come through and nearby targets would all show the same direction but the displacement of the 155.5 was more pronounced and I KNOW, this shooter reads wind at the top of the game.

The big issue was vertical where I would be pushed as much as 1 scoring ring further.

This Aug with the 308/200gr, the bumpy outs went away. Sure there was elevation but it was easy to confirm vs a condition as opposed to hanging on for dear life with the lighter bullet

The trend in F class is towards bigger and heavier bullets... WHY?

Whether the BC calculations account for it or not, I know mass matters once you go beyond 600m in bumpy air.

By the way, that 223/90 shot much easier on the prairies even with the wind in the 10 to 16 min range. Big air but it was dead flat - just left and right. Not much vertical as the range is well, you know.

And my drifts were near identical to 308/185 shooters as the program suggests.

Jerry

 

[Laurie]

In theory, the BC + MV combination is the sole determinant of wind drift. But that assumes that these are the only two factors and that they are set in stone. BC is only ever an approximation of one bullet's air drag in one set of conditions. It may vary a bit; the bullet design may suit one set of conditions and/or distance better than another. I prefer to use this the BC/MV combination as an initial guide and see how the bullet actually performs on the range. To be honest, I neither know nor for that matter care exactly what other factors change things at the margin as long as it works in most real-life conditions.

What it can tell us is that some combinations are most unlikely to perform well at long ranges and are simply best avoided. What it can't tell us is what particular bullet design shape allied to spin rate will or won't cope with terminal speeds just above the speed of sound. There is a lot of empirical evidence that ballistics program results understate wind effect for instance for many bullets as they drop under 1.1 MACH - but some are affected less than others.

What did surprise me a little, no actually a lot, when I first looked at external ballistics was the form factor which is the basic and true pointer to the bullet's design efficiency when allied to weight, or more precisely, sectional density and then in turn to comparable velocities. Take two bullets with identical form factors, ie their designs are equally efficient, but with different weights. That applies to Bryan Litz's work giving the 155.5gn .30 Berger BT Fullbore an identical i7 form factor value to that of the 210gn Berger LR BT, 0.988 in both cases. Note these are derived working backwards from retained speeds to average G7 BC to i7, not based on a desktop computer analysis of the shape.

Naturally, the 210gn bullet has a much higher BC than the 155.5gn after its higher SD is added to the mix, but we know that's offset by a lower MV. Calculate equivalent MVs based on the energy the different weights produce and we see 3,000 fps MV for the 155.5 gn model equates to 2,581 fps for the 210 both producing 3,108 ft/lb ME.

'Common sense' dictates that the pair will behave identically at these equivalent MV levels, only they don't. The 210 outperforms the 155.5 in the wind despite being 'equally efficient'. No matter how often I checked this out, I got the same result and eventually went to the guru himself, the self same Bryan L. He confirms this result which is why he always recommends going with the heaviest bullet within any efficiency bracket that the rifle and shooter are comfortable with.

 

[ShootDots]

Hey Laurie! You eloquently stated what I was attempting to say in my first reply (Reply #2) here.... I think we came to the same conclusion! Thanks!!

 

[22BRGUY]

Appreciate the clarification and info guys as it relates to this topic. In my 22br for longer range, Berger offers an 80gr and an 82gr bullet with very nearly identical BC's, but name the 82gr a "long range" bullet. My guess on that is both because of the profile and the extra 2 grain weight factor. Although 2 grains isn't much, it will have some beneficial effect I believe.