# Wind drift? How much does your bullet move?



## RobaloSunrise (Jun 10, 2011)

Another good article.

http://www.accurateshooter.com/shooting-skills/horizontal-wind-drift-vs-distance/

V/R
J


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## Wolf6151 (Jun 13, 2005)

**** I knew I should have paid attention in Algebra. This gives me a new found respect for the guys who shoot 1000 yd. competitions. Where do you get these come up sheets the article refers to? I assume they would be for each individual bullet at different velocities?


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## RobaloSunrise (Jun 10, 2011)

You get them through time and practice. There is no substitute for your own dope books.


V/R
J


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## THE JAMMER (Aug 1, 2005)

EXCELLENT ARTICLE. I have used ballistic software for many years, but that article was probably the best "layman's explanation" I have ever read.

WEll done Robalo. You've been doing some great stuff lately. I have been out of pocket for a while with rotator cuff, and am now wading through the stuff on canting. I've used levels on my scopes for years as well, but what I've read so far gives great geometric explanation of the phenomenon.

THE JAMMER


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## CHARLIE (Jun 2, 2004)

Also heavier bullet less drift.

Jammer hurry back you have been gone too long


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## RobaloSunrise (Jun 10, 2011)

Heavier bullets do not always drift less. Bullets with a higher BC drift less. 142 gr 6.5mm VLD's drift considerably less than 180gr 7.62mm flat base bullets do. Even though they weigh less.


V/R
J


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## CHARLIE (Jun 2, 2004)

Could have to do with more time exposure to the wind ya think ??


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## RobaloSunrise (Jun 10, 2011)

CHARLIE said:


> Could have to do with more time exposure to the wind ya think ??


You are right if you are referring to the differences in velocity between what a 6.5 x 284 could produce and what a 308 would produce. However if you adjust velocities for each until they are the same say 2900fps which is attainable by both 6.5x 284 and 300 win mag the lower BC of the 300 is greatly trumped by the high BC 6.5. When shooting distance it is all about BC. If you can push a .700BC bullet at 2800fps it will outperform a 400 BC bullet at 3000 all day long in both elevation and windage.

V/R
J


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## RobaloSunrise (Jun 10, 2011)

Ran it through my ballistics program and at 2900fps a 180grn 7.62 with a G7 profile of .202 has a drop of 35.56moa (372.34") and a drift of 11.96moa (125.28") at 1000yds with a 10mph wind from the 9oclock. At 2900fps a 140grn 6.5 with a g7 profile of .293 has a drop of 26.83moa (281.01") and a drift of 7.42moa (77.72") at 1000 yds with a 10mph wind from the 9oclock. About 2/3rds the movement. The 7.62 will have a longer flight time due to the increased drag and quicker deceleration which is due to the lower BC. So yes a longer flight time does effect the outcome but only due to the BC, if you use a higher BC 7.62 bullet then the results are the same as the 6.5. A 200 grn 7.62 vld at 2900 is getting close to the same as the 6.5 and a 205 grn should be almost the same.


V/R
J


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## CHARLIE (Jun 2, 2004)

A heavier bullet with the exact same everything and velocity will drift less with the wind than the lighter bullet. I have a question, are you saying that the lighter bullet will maintain velocity longer than a heavier bullet of the same design ?? My thoughts are that the heavier bullet will surpass the lighter bullet at longer ranges. The lighter bullet will lose velocity quicker.. and at some range the heavier bullet will surpass the lighter bullet.

Please do not get me wrong I am certainly not a know it all its just from years of being involved in the shooting game.. Have no access to programs or charts or tables.. just my thoughts..


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## RobaloSunrise (Jun 10, 2011)

CHARLIE said:


> A heavier bullet with the exact same everything and velocity will drift less with the wind than the lighter bullet. I have a question, are you saying that the lighter bullet will maintain velocity longer than a heavier bullet of the same design ?? My thoughts are that the heavier bullet will surpass the lighter bullet at longer ranges. The lighter bullet will lose velocity quicker.. and at some range the heavier bullet will surpass the lighter bullet.
> 
> Please do not get me wrong I am certainly not a know it all its just from years of being involved in the shooting game.. Have no access to programs or charts or tables.. just my thoughts..


Lot of variables but lets try to narrow it down. Let's assume the same VLD bullets in two weights 180 grn and 210grn, Sierra match kings. Let's assume same caliber, 7.62mm. Then yes the heavier bullet will drift less and retain velocity better. However let's add in another caliber and now a 142grn 6.5mm will retain more velocity and drift less than a 180 grn 7.62 the 210 will still outperform it. It is all about the ballistic coefficient of drag. It gets even more complicated when you add in high drag bullets like flat base. Bottom line is not all heavier bullets are better. this is especially true if you factor in recoil.

V/R
J


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## CHARLIE (Jun 2, 2004)

My point was only this , say a 168 gr 7.62 bullet vs a 142 gr 6.5 bullet of the exact same design at the same velocity the 7.62 will out perform the lighter bullet downrange.. velocity, drift, and drop..That was my only point.


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## Ernest (May 21, 2004)

BC is a function of mass, diameter, and drag coefficient. So yes, everything else being equal (in an imaginary world) a heavier bullet has a higher BC. Thus, it loses less velocity and bucks the wind. 

The ability of a bullet to sustain velocity is called BC. Weight (as in mass) is already factored into the BC. So, the take away message, shoot high BC bullets if you want to sustain velocity. 

The wind impact on a bullet is wind drag. Its not wind pushing on the side of the bullet. The nose of the bullet will always be at the center of pressure.


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## RobaloSunrise (Jun 10, 2011)

CHARLIE said:


> My point was only this , say a 168 gr 7.62 bullet vs a 142 gr 6.5 bullet of the exact same design at the same velocity the 7.62 will out perform the lighter bullet downrange.. velocity, drift, and drop..That was my only point.


He are the charts for both of the bullets you have mentioned here. You can see for yourself the BC (G7) is higher for the 6.5 than the 7.62. This causes the 6.5 to retain velocity and be less affected by cross wind than the 7.62. There is a excellent article on appliedballistics.com by Bryan Litz which covers the idea of scaling bullets. I order to reach the same trajectory as the 6.5 a 7.62 needs to be of the same design and weigh about 205grns. As I mentioned earlier it is all about the BC if everything else is equal.

Input Parameters
.308 Sierra 168gr HPBT MK

Powder Type:	
Powder Weight:	
Primer Type:	
Brass Make:	
C.O.L.:	
Rifle:	
Barrel Length:	
Shot Group:	
Notes:

TKO:	21.44
OGW / Muzzle:	1032.5 lb
OGW / Zero:	835.3 lb
IPSC PF:	487.20
BC	Bullet
Weight	Muzzle
Velocity	Zero
Range Sight
Height	LOS
Angle 
0.229 G7 168gr	2900	100	1.5 in	0


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## RobaloSunrise (Jun 10, 2011)

Why wont this let me post a spreadsheet?

Input Parameters
.264 Sierra 142gr HPBT MK

Powder Type:	
Powder Weight:	
Primer Type:	
Brass Make:	
C.O.L.:	
Rifle:	
Barrel Length:	
Shot Group:	
Notes:	

TKO:	15.53
OGW / Muzzle:	737.7 lb
OGW / Zero:	626.1 lb
IPSC PF:	411.80
BC	Bullet
Weight	Muzzle
Velocity	Zero
Range Sight
Height	LOS
Angle 
0.295 G7 142gr	2900	100	1.5 in	0


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## RobaloSunrise (Jun 10, 2011)

6.5

Range. In Drop. MOA drop Wind in Wind MOA velocity energy time
600 -72.68	-11.57	24.09	3.83	2021	1287	0.74
625 -80.83	-12.35	26.35	4.03	1988	1246	0.78
650 -89.53	-13.15	28.73	4.22	1955	1205	0.82
675 -98.78	-13.97	31.24	4.42	1923	1165	0.86
700 -108.61	-14.82	33.87	4.62	1891	1127	0.90
725 -119.03	-15.68	36.64	4.83	1859	1089	0.94
750 -130.08	-16.56	39.54	5.03	1827	1052	0.98
775 -141.75	-17.47	42.59	5.25	1796	1016	1.02
800 -154.10	-18.39	45.77	5.46	1764	981	1.06
825 -167.12	-19.34	49.10	5.68	1734	947	1.10
850 -180.85	-20.32	52.59	5.91	1703	914	1.15
875 -195.32	-21.32	56.23	6.14	1672	882	1.19
900 -210.56	-22.34	60.03	6.37	1642	850	1.24
925 -226.58	-23.39	64.00	6.61	1612	819	1.28
950 -243.42	-24.47	68.14	6.85	1583	789	1.33
975 -261.12	-25.57	72.45	7.10	1553	760	1.38
1000 -279.70	-26.71	76.95	7.35	1524	732	1.43


v/r
j


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## RobaloSunrise (Jun 10, 2011)

7.62

600 -79.78	-12.70	32.74	5.21	1800	1208	0.79
625 -89.11	-13.62	35.92	5.49	1759	1155	0.83
650 -99.13	-14.56	39.29	5.77	1720	1103	0.87
675 -109.86	-15.54	42.87	6.06	1680	1053	0.92
700 -121.34	-16.55	46.64	6.36	1641	1005	0.96
725 -133.62	-17.60	50.63	6.67	1603	958	1.01
750 -146.71	-18.68	54.84	6.98	1565	913	1.06
775 -160.68	-19.80	59.28	7.30	1527	870	1.10
800 -175.55	-20.96	63.97	7.64	1490	828	1.15
825 -191.38	-22.15	68.90	7.97	1453	787	1.21
850 -208.22	-23.39	74.09	8.32	1416	748	1.26
875 -226.12	-24.68	79.55	8.68	1380	710	1.31
900 -245.14	-26.01	85.30	9.05	1344	674	1.37
925 -265.33	-27.39	91.34	9.43	1309	639	1.42
950 -286.76	-28.83	97.69	9.82	1275	606	1.48
975 -309.51	-30.31	104.35	10.22	1241	574	1.54
1000 -333.63	-31.86	111.35	10.63	1207	544	1.60

I was hoping to get the data all in one spot but not gonna happen on this forum.

v/r
j


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## JuanGrande (May 29, 2010)

Great article. Now I got the itch to go to the rifle range this weekend.


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## CHARLIE (Jun 2, 2004)

I am making no further comment other than that is totally opposite to what I have seen with my own eyes.. but thats life.

Hang in there Ernest..


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## Ernest (May 21, 2004)

Charlie RE: free programs on the net (now on smart phones). 

They are easy to use, very accurate for practice purposes at reasonable distances, and allow you to print out some great little dope cards for the rounds. Plus, they allow you to do "red neck" chrony work by comparing your drop over a known distance with predicted drop for a given velocity. 

I'm a fan.


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## RobaloSunrise (Jun 10, 2011)

CHARLIE said:


> I am making no further comment other than that is totally opposite to what I have seen with my own eyes.. but thats life.
> 
> Hang in there Ernest..


Well Charlie that's why we all go to these forums, to have honest discussions and hopefully learn stuff. I learn something new on here about everyday.

I can also show you on the software where a heavier bullet would be better than a lighter bullet. However you won't be comparing apples to apples then. If you take a 130grn flat base spire point and put it up against a 168grn boat tail. Then you are going to see much different results.

Keep in mind we are changing calibers which has a lot to do with why the lighter bullet has better BC than the heavier one. If we stayed in the same caliber the heavier bullet would be better then the lighter one.

Like I said at the start a lot of variables.

V/R
J


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## CHARLIE (Jun 2, 2004)

RobaloSunrise

I do have another question. In your opinion which bullet would deflect more because of wind at 50 yards. A 22 long rifle standard velocity (match)or a 45 cal 185 grain wadcutter at their respective velocities which I am not sure of but definately not the same.


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## RobaloSunrise (Jun 10, 2011)

If you are shooting 185grn +P they are around 1150 fps and a standard velocity 22 is about 1100 fps. The only bullet data I have Is from m big book of bullets and it doesn't give me wind drift for pistols. The 22 shows 1.29" at 50yds in a 10mph wind. I used my best guess on my ballistics software and it gives me 1.09 for a 200 grn round nose at 770 which is what the only swc185 I could find was.


V/R
J


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## CHARLIE (Jun 2, 2004)

Well the 185 gr wadcutter not plus P it is a match bullet somewhat less than 830 FPS. The 22 moves much more that the big ole fat 45 in a crosswind. Thats from experience.


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## RobaloSunrise (Jun 10, 2011)

Charlie, what is your argument here? If you read back you will find that I stated they don't always drift less, not that they couldn't drift less.



RobaloSunrise said:


> Heavier bullets do not always drift less. Bullets with a higher BC drift less. 142 gr 6.5mm VLD's drift considerably less than 180gr 7.62mm flat base bullets do. Even though they weigh less.
> 
> V/R
> J


If you remembr me writing this you will see that I stated it wasn't the weight it was the BC that caused a reduction in the movement. I can find a lot of heavy bullets that will drift less than light ones.

There are a number of different variables that need to be filled in before blanketing that a heavier bullet will always drift less. Caliber, velocity, bullet design, BC, weight, all contribute to whether a bullet will buck the wind or not. Bullets with a high BC will always trump a bullet with low BC regardless of weight. A 6.5 142grn bullet is a heavy for caliber bullet. When scaled up to 7.62 you end up with a 229grn bullet which would equal or better the 142. Below that weight you get a lower BC and performance which is inferior to the lighter bullet. Here is the math used to scale a bullet to the 142.
7.62/6.5 = 1.1723
7.62 x 1.1723 cubed = 228.77 grn

If you are arguing that a heavier bullet always drifts less. Well I say it doesn't, I say it is a function of the BC and that a high BC bullet will always perform better than a low BC bullet.

V/R
J


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## prarie dog (Feb 28, 2011)

This is a very good article with a wind chart about two thirds of the way down from the top that demonstrates the difference between the 175 SMK 30 cal and various 6.5 offerings in the straight 260, the 260 AI and the 6.5-284. The nice thing about the chart is the comparisons are made at 1000 yds. so it's easy to see the drift differences between the bullets and rounds. The real nice thing about the 6.5's is they are easier to shoot than thirties because of the light recoil. Back in the 70s I was involved in large bore position shooting and some silhouette and benchrest score shooting. At the time we used the 30's almost exclusively because of the real consistent, fine shooting 168 SMK. Nowadays we have many really fine shooting 6.5, and 7 mm bullets to choose from. The poor old 30 has been kicked to the curb. Many ex military guys have a hard time giving up on them but it is the fact. 
BTW, Charley my offer to take you Prairie Dog shooting is still open, bring your thirties and I'll bring my 6.5's and we'll see which is top dawg. http://www.6mmbr.com/gunweek046.html


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## CHARLIE (Jun 2, 2004)

Prarie dog

Naw sorry but I am past my prime sounds like it wouild be fun tho.. And I must say some very interesting articles and charts and infromation.. Go get em


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