Wind Drift

[goodgrouper]

[ QUOTE ]
Higher BC (heavier) virtually ALWAYS have longer time of flight, but will have less wind drift.

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You may be off on another tangent here I didn't catch but if you are stating (and you're probably not) that higher bc bullets have longer time of flights compared to lighter faster bullets than I would like point out that that is only true to short distances. At some point downrange, the lighter and lower bc bullet will not get to a target as fast as the slower, heavier, higher bc bullet will.

Take for instance the 40 grain 22 caliber bullet at mv of 4400 and compare it to the 80 grain 22 caliber bullet at a mv of 3400 fps. Although the 40 grainer starts off 1000 fps faster at the muzzle, it is going slower than the other bullet at the 1000 yard target. Differences in t.o.f. are less than 1 second but are still in favor of the high bc bullet winning the race to the 1k target.

 

[bjlooper]

Good grouper you are correct who ever wins the race will drift less and drop less at that given distance. if you back up to 400 yd then your 40gr bullet wins and drifts less and drops less at 400 yds.
Dr B

 

[bailey1474]

[ QUOTE ]
you back up to 400 yd then your 40gr bullet wins and drifts less and drops less at 400 yds.
Dr B

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Might want to check your drift #s. I think you will be suprised!!!

 

[Eaglet]

bjlooper,
You're right!!! and also would have the same energy. <u>The only thing</u> that would not be the same would be the MOMENTUM with is defined by Ballistic Explorer as: [ QUOTE ]
<font color="blue"> Momentum
An indication of a bullet's knockdown power is momentum. Doubling either the weight (mass) or velocity of a bullet doubles its momentum. <font color="green">Clearly it's energy that makes bullets deadly to game, </font> <font color="purple">yet it's momentum that knocks game off its feet or knocks metal targets over. </font> </font>

[/ QUOTE ]

 

[abinok]

yep

 

[Jon A]

[ QUOTE ]
If weight is added to a bullet and the shape remains the same, then the bc will go up because the bullet is getting longer while the shape is staying the same.

[/ QUOTE ]
It doesn't have to get longer. Fill the same jacket full of tungsten instead of lead and the BC will go up with no change in shape or length. The weight by itself will increase the BC since BC is a function of weight (and diameter and form factor). That's what he was saying.

With the same meplat, ogive and boattail, adding length in the shank changes the form factor very little and BC will go up pretty much in proportion to the weight. Of course the length allows you to use a longer ogive and boattail, etc, so you can improve the form factor while you're at it. But you don't have to in order to increase the BC.

 

[Shawn Carlock]

I have a customer that I set up a pair of balistic twins for. 1 is a 338 Lapua shooting 225 gr Accubonds @ 3000 fps, the other is a 6.5-284 shooting the Hornady 140 Amax @ 3000 fps. These two bullets fired both at 3000 fps also have identical BC. He has thus far shot out to 1148 yards using the same drop chart. All other things being equill BC and velocity will predict drop. Weight, form functions, diameter, etc directly bear on BC but singulary may not mean much as the case above a 225 grain bullet @ 3000 fps does not always shoot flatter than a 140 gr. While heavier slower bullets that have high BC's drop more than a lighter flatter faster shooting bullet alot of times, the higher BC bullet almost always has way less wind drift and to me that is the name of the game.

 

[Meister]

A BC to BC comparison such as shawn has done will tell quite a lot, one thing being that if one bullet has a better tip-over balance it will retain its energy better because it doesn't "show" as much bearing surface to the wind as it drops on target at long range. This is another variable to consider when comparing two bullets of similar bc in different calibers or manufacturers.

If a bullet isn't properly stabilized and balanced it will slow faster and group poorly at extreme distances. This is one of the reasons I have stayed away from 2 high bc bullets in favor of a lower bc highly balanced bullet. By no means am I knocking a high bc bullet, just my personal preference.

 

[ajhardle]

I posted a similar thread and might have some insight. If someone has cartridge chosen, it is wise to chose the longest, most slippery bullet made that will stabilize in his rifle. B.C. can be misleading. It's form factor that is important, because bigger bullets have higher b.c.'s. A smaller bullet with a lower b.c. but a better(lower numericaly) form factor will whoop all over a less streamlined heavy bullet. form factor=s.d./b.c.

 

[ajhardle]

An even better choice is to buy a barrel with a smaller hole poked through it. As long as you can stuff nearly as much powder behind the smaller diameter bullet, with a similar shape, it will have less wind drift. (for instance, a .284 v 6.5x.284, or 7rum v .338lapua). Run it through your ballistic calculators. Assuming similar energy, meaning smaller bullets go faster, the smaller diameter always win. Scale it down as much as you want, the smaller wins out to a range beyond most people have any business shooting at. Depending on case size, that range can easily exceed 2000 and even 3000 yards. There is a cost of barrel wear.

 

[WildRose]

An even better choice is to buy a barrel with a smaller hole poked through it. As long as you can stuff nearly as much powder behind the smaller diameter bullet, with a similar shape, it will have less wind drift. (for instance, a .284 v 6.5x.284, or 7rum v .338lapua). Run it through your ballistic calculators. Assuming similar energy, meaning smaller bullets go faster, the smaller diameter always win. Scale it down as much as you want, the smaller wins out to a range beyond most people have any business shooting at. Depending on case size, that range can easily exceed 2000 and even 3000 yards. There is a cost of barrel wear.

This post made my head go "tilt" all five times I read it.

I then went ove to my favorite handy ballitics calculator to compare a couple of extremes and see how the numbers shook out.

Ballistics Calculator v1.0

Ballistics Calculator v1.0

I get 56" wind drift at 1000 with the 208gr Amax at 3000FPS and 179" wind drift with the .32gr 4000fps .204 which is about what I expected which would be the opposite of what you are asserting above if I'm reading it correctly.

That's 10 Feet more wind drift with the smaller, faster, lower BC bullet.

High BC bullets resist wind effects far better than Lower BC bullets, even when the lower BC bullet is traveling at much higher velocity.

Even using a direct apples to apples example with the 165gr Amax at 3,400fps you get a wind drift of 71.7 which is 25% Higher than with the same exact bullet in 208gr's.

Ballistics Calculator v1.0

You also run into the fact that there are limits on just how fast any bullets can be pushed.

 

[ajhardle]

Try it again, but this time consider a similar amount of energy. Of course almost anything shot with 80 gr. of powder will out shoot a .204 ruger.
Let's use a 243 diameter bullet in the same size case for comparison. this is just to show a trend, and there are limits. But if your case can shoot a 208 gr at 3000 fps, it should shoot a 115 at 4035 ffps. Same case, necked down, means similar energy.
With the same energy (4155ft-lbs) this .243 drifted only 40 ". a worthwhile improvement.
Also, assume similar class of bullets. A flat base varmint can't compare with a secant vld.

 

[ajhardle]

switching to a 165 gr. is not scaling down. It is using a stubbier bullet of a same diameter. Bad for any measure of long range ballistics. If your stuck with a bore diameter, get the longest bullet you can stabilize. If you can get a new barrel, a smaller diameter can help.

 

[WildRose]

Try it again, but this time consider a similar amount of energy. Of course almost anything shot with 80 gr. of powder will out shoot a .204 ruger.
Let's use a 243 diameter bullet in the same size case for comparison. this is just to show a trend, and there are limits. But if your case can shoot a 208 gr at 3000 fps, it should shoot a 115 at 4035 ffps. Same case, necked down, means similar energy.
With the same energy (4155ft-lbs) this .243 drifted only 40 ". a worthwhile improvement.

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.