Bullet weight vs Wind Drift

[Travelor]

Let's start the New Year with a rather interesting debate.

What are your thoughts about the wind drift of bullets such as a 22 caliber 80 grain as opposed to a 30 caliber 190 grain bullet at 1000 yards.

My thoughts are that a lighter bullet with a high BC and high MV should drift less at 1000 yards than a heavier bullet with a lower BC and lower MV. Look at the ballistic charts such as http://www.mega.nu/traj.html before you answer.

Let's hear your arguments and give facts not just opinions.

And let the games begin.

 

[BHarvey]

Take two ping pong balls and fill one with whatever to make it heavier, the tie a string to them and watch which one blows around easier.

Wind drift is all about the 'delay' time, air vs vacuum.
You would think 200 fps more velocity would make a huge difference in wind drift, but with the same bullet, that 200 fps only nets around 1 moa less drift, and that is only up to a certain point.

The 200 fps at the muzzle equates to around a 2/3 difference at 1k. Or around 140 fps difference.

A faster bullet has a higher % of velocity loss than a slow bullet. So while yes, the faster the same bullet is, it will have less drift in supersonic flight, the difference is not that large.

 

[Cheechako]

facts not just opinions.

Input whatever figures you want into a ballistic program, click on "calculate" and out will come the facts. Ballistics is pure physics. Physics is facts.

JMHO

Ray

 

[jerrysharrett]

A little weight makes a lot of difference in drift. The following are a couple of calculations I had made earlier today, one is a 130 grain 6.5mm Berger the other a 88 grain HBC 6mm Berger.

These calculations are for 600 yards in a 10 MPH cross wind.

The 6.5/130g at 2800 fps drifts 21.4" at 600,
the 6/88g at 3030 fps drifts 32.4".....a stark difference for just 230 fps difference in velocity!

 

[Cheechako]

Jerry

I think you'll find that the big difference in wind deflection,not drift) between those two bullets is a product of the BC.

A BC of .388 vs a BC of .595 is a huge difference.

An 88 grain bullet and a 130 grain bullet with the same BC at the same velocity will exhibit the same wind deflection. A difference of 230 fps will result in a wind deflection difference of only 1/2 MOA.

Leave everything else the same but substitute a .277 Sierra SP bullet for the 6.5/130 and see what you have.

Ray

 

[Dirtball]

Ray is 100% correct, same BC and same velocity equals SAME wind drift, no matter if the bullet weighs 80gr or 280gr. Where all of this comes into play is that you can drive small cal lower BC bullets at much faster velocities. When you do this you shorten the time of flight which shortens the time the wind has to effect the bullet flight. Which to some degree compensates for the lower BC.
Dave

 

[Forum Boss]

Ray is right... but the complete answer is a little more complicated because:

1. Oftentimes Bullet BC is calulated from a model, not based on actual observations, so it may be too high or too low, as stated.

2. BC, as an index of bullet drag, is dynamic. This means that BC can and often does CHANGE during flight, and the degree and rate of change may vary between two different bullets with the same nominal BC.

3. BC is not an absolute. BC varies with launch speed, as Sierra Bullets shows with their "multiple BC" data tables. Thus, when comparing the BC of different bullets, you also, ideally, need to know what is the MV of each bullet and how that affects the BC you "plug in" to your ballistics programs.

Having said all that, if you start with accurate, test-confirmed BCs that apply to the actual muzzle velocities you're shooting, bullets of equal BC should exhibit the same wind drift.

In the real world, this is sometimes not the case, for all the reasons mentioned about,BC is guesstimated, BC is for a different speed window etc.).

 

[ThunderDownUnder]

Its all about the mass, velocity and drag coefficient of the bullet or maybe we know it as the bullet's BC. Its complex and thankfully as shooters, manufacturers give us the bullet's BC, we just need to hope that the numbers given are real world figures.

Those that want a more in depth explanation look here: http://www.answers.com/topic/ballistic-coefficient

Below is a small copy and paste from this site.

Bullet performance

The formula for calculating the ballistic coefficient for a bullet is as follows:[1][2]

BC = SD/i = M/,i x d^2)

where:

* BC = ballistic coefficient
* SD = sectional density, SD = mass of bullet in pounds or kilograms divided by its caliber squared in inches or meters; units are lb/in2 or kg/m2.
* i = form factor, i = drag coefficient of the bullet/drag coefficient of G1 model bullet,G1 drag coefficient = 0.5190793992194678)
* M = Mass of object, lb or kg
* d = diameter of the object, in or m

This BC formula gives the ratio of ballistic efficiency compared to the standard G1 model projectile. The standard projectile originates from the "C" standard reference projectile defined by the German steel, ammunition and armaments manufacturer Krupp in 1881.[3] The G1 model standard projectile has a BC of 1.[4] The French Gavre Commission decided to use this projectile as their first reference projectile, giving the G1 name.[5][6]

A bullet with a high BC will travel farther than one with a low BC since it will retain its velocity better as it flies downrange from the muzzle, will resist the wind better, and will “shoot flatter”,see external ballistics).[7]

This difference in trajectories becomes more critical at longer ranges. For some cartridges, the difference in two bullet designs fired from the same rifle can result in a difference between the two of over 30 cm,1 foot) at 500 meters,550 yards). The difference in impact energy can also be great because kinetic energy depends on the square of the velocity. A bullet with a high BC arrives at the target faster and with more energy than one with a low BC.

Since the higher BC bullet gets to the target faster, it is also less affected by the crosswinds.

The transient nature of bullet bcs

Variations in BC claims for exactly the same projectiles can be explained by differences in the ambient air density used for these BC statements or differing range-speed measurements on which the stated G1 BC averages are based. The BC changes during a projectile's flight and stated BC's are always averages for particular range-speed regimes. Some more explanation about the transient nature of a projectile's G1 BC,it rises above or gets under a stated average value for a certain speed-range regime) during flight can be found at the external ballistics article. This article implies that knowing how a BC was established is almost as important as knowing the stated BC value itself.

For the precise establishment of BCs,or perhaps the scientifically better expressed drag coefficients), Doppler radar-measurements are required. The normal shooting or aerodynamics enthusiast, however, has no access to such expensive professional measurement devices. Weibel 1000e Doppler radars are used by governments, professional ballisticians, defense forces, and a few ammunition manufacturers to obtain exact real world data on the flight behavior of projectiles of interest.

 

[Forum Boss]

The G1 drag model is only one of many models used for calculating bullet ballistics, and some experts believe that it's not necessarily the best model.

Calculating BC based on design models is different than calculating actual measured drag by running multiple chronographs at widely separated distances. For example, with the Tubb DTAC bullets, "model-calculated" BC was slightly higher than the BC determined by Henry Child's field test using multiple inline chronographs.

I'm not posting this to refute any of the above discussion...only to further illustrate that the BC we are given by a bullet manufacturer may prove to be different than a "real-world" BC.

 

[ALppc]

So knowing all that. For 600yds would you choose a bullet that,theoretically) gave zero vertical and 2” more wind drift,more accurate) or a bullet with two inches of vertical and 2” less drift.

Al Barnhart

 

[confuzed]

Sometimes its just real world results that convince myself, after a tactical match on Sunday, for kicks we shot at the gong at 1200 yards the wind had kicked up hard,most of the guys shooting 308s with 175 matchkings had almost 8 minutes of left wind on their gun I was shooting a 6xc that day 107 mk at 2975 with 6 minutes on the gun

 

[FTRshooter]

So knowing all that. For 600yds would you choose a bullet that,theoretically) gave zero vertical and 2” more wind drift,more accurate) or a bullet with two inches of vertical and 2” less drift.

Al Barnhart

An interesting question and one that I have been asking myself lately. My answer currently is to use a bullet that has more vertical but less wind. I can control the vertical and I rarely lose points to bullets that went low or high unless I had a face or rear wind. If I had vertical issues, I would check my handloading technique.

On the other hand I have lost a lot of points to horizontal displacement, either in the pick ups but even more often in the let-ups. So my thinking has been to reduce the wind drift. In a given caliber there is really only one way to do that with the same shape and that's to increase the SD of the bullet.

There are two ways to accomplish that, either use a longer heavier bullet or use a denser material. Since I don't seem that have any DU on hand and gold is pricey, I will use longer bullets. Either way, the MV of the bullet will diminish because of the increased weight, but it is hoped the higher BC will make up some of the lost vertical. The prize is the reduced drift.

That's my current thinking.

 

[GermanS1]

I take the opposite view on Al's question,a very thought provoking question with no single 'right answer'). I assume he means that with the very best load possible for the theoretical bullets, one will always show 2' of vertical and the other will always show zero vertical. The zero vertical bullet will also,in the example) always drift a bit more in a given wind speed. In that scenario, I'll take the zero vertical bullet each time.

To me, the whole objective of the sport,long-range prone shooting) is to shoot better and read wind better than the competition. If I do that job right, then I've earned the win; if not, then I need to work harder. The 'zero vertical' bullet would let me test my skills with less concern for bullet-induced problems,vertical dispersion). The low vertical dispersion would keep me in the meatier part of the 10 ring or X ring and allow a higher score if I read the wind correctly.

In fact, Al's question is a very shorthand description of my load development method. I gather a few bullets that should be good for the cartridge in question and work on developing loads by culling through a lot of loads at 200 or 300 yards, then take the good ones to 600 or 1000,depending on the use intended) and look for the lowest mean vertical dispersion. The wind drift doesn't enter into it too much because all the bullets will be roughly similar. The load with the lowest mean vertical dispersion allows me to work on my wind reading and shooting with the highest level of confidence.

Great question, Al!

 

[Bryan Litz Ballistics]

Al's question really does get to the root of bullet/rifle optimization. I've had this conversation with many shooters, including the moderator. As with many complicated questions, the answer is: it depends.
If you're shooting on a dead calm day with no wind, reach on the 'golf bag' and screw on the club,barrel) that shoots the ammo/bullets with zero vertical and are more wind sensitive. If the conditions of the day are windy, pull out the club that has a little vertical, but minimizes the wind deflection.
Application based optimization in shooting is about identifying the greatest sources of error, and choosing the best equipment to mitigate them. The trick is that 'the biggest source of error' isn't a fixed thing, it literally changes with the weather.

-Bryan

Edited to add:
I went from the forum to the daily bulletin and saw this headline:

New Project Rifle — Our 6-6.5×47 + 6.5×47 Switch-Barrel

Sounds like an experiment in optimization to me! Shoot the middle weight flat based bullets in the 6mm barrel in matches when it's calm, maybe up to 600 yards. When the wind blows, screw on the 6.5mm club and choose from the high BC 140 grain class of bullets.

 

[Lbart]

Most competitive shooters worry too much about wind drift differences between bullets. They should defiantly be more concerned with the vertical groups they can fire. What is not considered much is the fact we shoot at round scoring rings.

Think about this...the X/ten ring is widest at 3 to 9 o’clock. If your load will shoot a zero elevation on the F-Class 10-ring target the target is 10” wide and you only have to dope the wind +or- 5”. If your load shoots a 10” elevation then your worst case 10-ring becomes zero inches wide in order to keep all shots in the ten-ring. I know I can’t dope the wind to zero inches.

Larry Bartholome
Team Berger

 

[spclark]

'Application based optimization in shooting is about identifying the greatest sources of error, and choosing the best equipment to mitigate them.'

That same approach could be said to work for just about anything!

Shortened to an epithet: 'Use the RIGHT TOOL for the JOB!'

Bryan, I like how you think....

 

[Forum Boss]

Most competitive shooters worry too much about wind drift differences between bullets. They should defiantly be more concerned with the vertical groups they can fire. What is not considered much is the fact we shoot at round scoring rings.

Think about this...the X/ten ring is widest at 3 to 9 o’clock. If your load will shoot a zero elevation on the F-Class 10-ring target the target is 10” wide and you only have to dope the wind +or- 5”. If your load shoots a 10” elevation then your worst case 10-ring becomes zero inches wide in order to keep all shots in the ten-ring. I know I can’t dope the wind to zero inches.

Larry Bartholome
Team Berger

GREAT Advice from Larry. This should be printed and posted on every range clubhouse door. If we shot at square scoring 'boxes' the story would be different. But with circles, you want to stay in the middle of the target vertically.

 

[FTRshooter]

I live to learn.

I was thinking that Al meant for the choices to be between a bullet that dropped more but deflected less,like a heavier bullet with a higher BC,) and a bullet that dropped less but deflected more,like a lighter bullet but with a lower BC.)

I was not aware that a bullet that had a higher BC would automatically display greater tendencies to vary in elevation. I'm learning new stuff here.

From my experiences, I detected a trend to have groups that are oval, horizontally. So, my thinking was that I was loading properly and holding properly and that I needed to work on my wind reading more and also see if I could minimize the effects of the wind.

So, I was thinking of using a heavier bullet with a higher BC, but now you have me thinking that's the wrong thing to do as it will introduce elevation problems. I will have to reflect on this.

 

[GermanS1]

FTR - the question was on a hypothetical basis, there is no reason to think that a higher BC bullet will necessarily display more vertical dispersion than a lower BC bullet. It's an interesting premise for discussion, but not a hard fact at all.

When you're testing ammo you'll find some bullets/loads give more vertical dispersion than others. If by change you find a load with an accurate, high BC bullet that also has low vertical dispersion that's the holy grail!