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Check out the ballistics chart from Pointblank, for a 300gr .375 Swift A-frame at 2600 fps..  If the wind was gusting between 10 and 15 mph, you could easily expect a half inch difference in POI between shots. If it was actually gusting between 0 and 15 mph, it could be as great as 1.5 inches. This is something I struggle with all the time during load development. I have lived in or near the mountains most of my life, and its difficult to find a day with a steady wind, let alone no wind. Some days I'd just about kill to get access to an indoor range like Saeed's! Cheers, Canuck | |||
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C, Please explain to me the difference between the first set of conditions which you posit, and the second. Kudude | |||
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Don't know where it came from but Remington has drift values in the ballistics section on their web site. ------------------------------- Will Stewart / Once you've been amongst them, there is no such thing as too much gun. --------------------------------------- and, God Bless John Wayne. NRA Benefactor Member, GOA, N.A.G.R. _________________________ "Elephant and Elephant Guns" $99 shipped “Hunting Africa's Dangerous Game" $20 shipped. red.dirt.elephant@gmail.com _________________________ Hoping to wind up where elephant hunters go. | |||
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Sure, I routinely shoot in 8-12mph winds, that's just the way it is in the mountains. On windy days I feel good if I can hold 1/2" groups w/ my varminter & 1 1/2" w/ my big game rifles. Yeah wind is a real bitch.  LIFE IS NOT A SPECTATOR'S SPORT! | |||
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Absolutely the wind can and does effect vertical as well as horizontal. the bullet falls at 16 fps2 or so, and the impact of wind up or down on the top or bottom, as compared to the two lateral sides of a bullet, makes the same effect as measured by force vectors. Forget the problem of half an inch or even an inch. You have an African rifle, not a teeny weeny varmint gun. I trust any animal you would throw a bullet at has at least an extra 1.5 inches of kill zone for each 100m or yds you are away from the animal. and at 2840 fps, you can be sure that your animal will not quibble about an inch or two up, down, or sideways. Jameister | |||
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this is just why the best high power target shooters are the best judges of wind. Trajectory is easy, you know how far, you know the drop, but the wind changes all the time | |||
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Mike, With that cartridge and load your accuracy is well within minute of anything you want to shoot with it. Perhaps it does shoot 7/8" and you had a bad day. 1.25"-1.5" would make me very happy. A big moose, bear, eland whatever will never know the difference. Regards, Mark MARK H. YOUNG MARK'S EXCLUSIVE ADVENTURES 7094 Oakleigh Dr. Las Vegas, NV 89110 Office 702-848-1693 Cell, Whats App, Signal 307-250-1156 PREFERRED E-mail markttc@msn.com Website: myexclusiveadventures.com Skype: markhyhunter Check us out on https://www.facebook.com/pages...ures/627027353990716 | |||
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When I got up this morning, the wind was absolutely dead calm, so I snuck out to the range for about an hour. At 100 yards, 3 shots went into .8", and 2 shots at 200 yards were only 1 1/2" apart. Confidence in my shooting has been restored. | ||
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Just came from playing around a little with the ballistics calculator. The numbers were not meant to be exact, but what I was saying was: Scenario A: wind steady at 10mph hour, gusting up to 15mph, assuming exact same POA for all shots, consistent wind direction. A shot fired while wind at 10mph would drift about an inch from expected POI. A shot fired during a gust of 15mph would drift up to 1.5 inches from expecte POI, or about a half inch further. Differential wind drift alone COULD account for up to a half inch increase in group size over what you would normally achieve in still conditions. Scenario B: wind varying from still to 15 mph. Wind consistently from same direction. Same POA for all shots. Wind drift alone COULD account for up to 1.5 inches larger group than you'd expect in still conditions. (ie. bullet #1 fired during still conditions, strikes expected POI. Bullet #2 fires during a gust of 15 mph strikes target 1.5 inches from expected POI, etc). Of course, none of this is exact. It would depend a lot on your usual group size, what direction the bullet was tending to when it left the muzzle (ie. if it wasn't going to strike a dead bullseye), relative to the wind dirction, etc, etc. I just keep it in mind on windy days. It really only makes a difference when developing loads, since if the wind is variable my group size may be more a function of the conditions than the variation in powder charge, seating depth, etc, etc, etc. Cheers, Canuck | |||
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Weight plays no role in wind drift. There are only two things that are of importance - speed and ballistic coefficient. The vertical component of wind drift is so small that it plays no role at hunting distances, unless you hunt on the other side of 500. | |||
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"the horizontal drift component is roughly proportional to the wind velocity and proportional to the sqaure of the range while the vertical component is roughly proportional to both the wind velocity and range". from Rifle Accuracy Facts by H. R. Vaughn montero | |||
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Last year I did load development on a 243. I had the holes all touching at 100 yds. When the owner shot the same rifle, he got 2-4" groups until he remembered what I told him about letting the barrel cool between shots. Then he was able to get much better. JD | |||
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There are two ways I am aware of that Ballistic Coefficients are obtained. The first one (which was used the most prior to good Chrony's and calculators) is to take the Sectional Density of a given bullet and divide it by an accepted form factor for its shape. The other is to shoot the subject bullet at known distances and compare it's trajectory and velocity to a perfect mathmatical model. Since bullets decelerate and ballistic coefficients change with velocity often an average over expected useful ranges is calculated from these empirically obtained values. Ballistic Coefficients by definition are the bullets efficiency to cut through the air. In short the higher the BC the less drift you will experience at the same velocity. | |||
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Alf, your qoute of McCoy is out of context and not relevant to the issue. What McCoy was addressing in that text is the issue of aerodynamic jump, or the effect of crosswind on vertical deflection of the bullet. Regarding your comment about mass, it is relevant only as it relates to BC. Wind deflection is a function of drag. Two bullets with the same BC will deflect the same regardless of weight.  If yuro'e corseseyd and dsyelixc can you siltl raed oaky? | |||
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That is correct. However, what I believe Alf was hinting is that for the same shape, the bullet with the higher SD will have a higher BC. Low SD bullets must have a more efficient shape just to match the BC of a higher SD bullet--to "make up for" their lack of weight in a given caliber. | |||
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I think everyone agrees the ballistic coefficient is the most telling parameter in a bullets ability to handle a cross wind. Now I wonder how closely the BCs calculated using the Sectional density divided by form factor method would correlate with one obtained by empirically from the range with a particular bullet? Personally I am not so sure that a solid copper, a polymer tipped or a bonded bullet with low lead content would be all that close. These bullets are longer than classically constructed projectiles of equal weight. Is not the length of these projectiles important?  | |||
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Not really. Shank length contributes very little to drag though it does have an effect on interior ballistics. The factors of form, weight and diameter are interrelated but not exclusive. What one bullet may lack in SD might be compensated for somewhat by form in another, thus different bullets may have the same BC. What bullet manufacturers advertise for BC may or may not be your experience though the point is of little note for typical shooting endeavors. We are saddled with BC for better or worse, and when you use such a value remember it represents a practical totality of the bullets ability to overcome drag. It is convenient and it is approximate. True BC value is determined by proper evaluation at the range or lab and is something few of us are equipped to examine. Those of you who dabble at this in more depth may run across the modern ballistic term of Cd, or coefficient of drag. It is a measure of drag value resulting from form, nothing else. Aeroballisticians use additional factors such as weight and atmospherics to determine what will occur downrange, but I mention this to bring to your attention that while BC is known to morph to different values from one circumstance to the next, Cd does not. And a significant factor regarding this is that Cd is inversely proportional to Mach Number. If yuro'e corseseyd and dsyelixc can you siltl raed oaky? | |||
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It might be close, it might not. But that has nothing to do with the sectional density part of it. That part is simple physics and is easily the most accurate portion of the whole picture. What actual testing will get you is a more accurate form factor. | |||
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Alf, my mistake on that regarding the AJ comment I made, missed the second part of the question in the original post. Sorry.  Crosswinds do indeed cause vertical deflection, just thought the question was in regards to drift. I will make another comment however.
D=W(T-Tv) In context of the formula for deflection, I take small exception to that part of the comment which I highlighted above. The value (T-Tv) is NOT TOF, it is lag time. Generally speaking increased velocity WILL reduce drift, but it is NOT because of shorter TOF, it is because of a smaller value for lag time. If you read McCoy's book you might remember this: "Cd is inversely proportional to Mach Number." Reduced drag is the reason, not reduced TOF. If yuro'e corseseyd and dsyelixc can you siltl raed oaky? | |||
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not so, I believe. a .22 lr bullet fired at 1255 fps will reach 100 yds in .269 secs and the wind deflection in a 10 mph crosswind will be about 5.2 in. a bullet simply dropped from the hand at the instant the gun is fired woul fall about 14 in during the .269 second time of flight. thus, it would be exposed to the wind for the same length of time as the bullet fired at the 100 yd target. we probably now intuitively that the .22 lr bullet simply dropped from a height of 14 in in a 10 mph crosswind will not drift sideways by about5.2 in. if experimental proof is needed, then the simple expierence of droppimg a .22 lr bullet from a height of 14 in in a moderate breeze will be enlightning.  inspired in Norma's Reloading Manual, Exterior ballistics chapter, by William C. Davis Jr. Montero | |||
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Alf, The fact that weight has nothing to do with wind drift is easy to prove. Use any ballistics program you like. Set up the data of any bullet you like. Check the wind drift values and then change the weight as much or as little as you like. Only changes in BC and speed will affect wind drift values. As for making a case for Sd affecting wind drift...  | |||
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Alf,
The above is not what I said. The question was whether it is normal for a heavy bullet to be moved that much by wind. I said weight does not affect wind drift and that is undeniable fact. The factors you mention above go to BC and I agree with you: BC greatly affects wind drift. I said so in my first post. Whether you use 6DOF code or a commercial ballistics program, these two facts remain true. DigitalDan has a good handle on this subject, listen up.  | |||
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So it would seem all form factors are derived from an experimentally obtained Ballistic Coefficient. You would get the Form Factors by taking the inverse of the BC divided by the SD. Right? Since BCs are unitless why not just develop form factors based on the weight of the bullet? | |||
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I'm thinking there is more of a debate here on points of perspective than physics, sort of like taking different roads to the same house. In and of itself weight is a player in the calculation of BC, but not the whole picture. It is the synergy of form and weight in play with the other more subtle aspects such as velocity, atmospherics, and even gyroscopic stability factors. An extreme comparison illustrates the benefit of weight wherein Hornady's 25 grain .17 cal bullet has a BC of .187(advertised), and their .44 cal. 300 grain bullet is advertised at .245 for BC. For those enamoured with sleek forms typical of boat tail spitzers this must be depressing news! That said, I doubt anybody wants to have a .44 Mag varmint rifle.  The limiting factor on all of this IMO, is that there are practifcal limits on twist rates that are necessary to stabilize the projectile if higher BC's are sought by adding weight. In theory one may achieve very high BC's with very small bore diameter, but in practical terms it doesn't work out that way. I assure you that if somebody could make a .17 cal bullet with a BC of 1.0 it would have been done long ago. Well, as ALF has indicated there is a whole lot going on in a bullets flight and most of it has a direct impact on the net result on target. It all influences BC. The confluence of all those details leads to a real world measure of a bullet's ability to resist drag and I think that is Gerard's point. In the end we look at BC to calculate or project what can reasonalby be expected of the bullet as it travels down range. Sometimes when I get lost in the various books on the subject I'm left to wonder how anybody can hit anything at any range with a gyroscopically stabilized projectile. It is difficult enough to understand the influences of one aspect let alone ALL of the factors at play. It is impossible to explain it fully in this format, thus when somebody reads these threads it is best understood that any discussion on exterior ballistic must by the topical nature of things, be focused on one or two points and does NOT cover all the ground of the subject. If yuro'e corseseyd and dsyelixc can you siltl raed oaky? | |||
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ALF, as i mentioned in my post, the explanation I gave as to support the idea that wind drif is not a function of time of flight, was taken from the chapter "Exterior Ballistics" in norma's Reloading Manual, which was written by William C. Davir Jr. On your last post you say that
And I would just like to remark that it was him, and not me, that gives the analogy that raise the following comment from you
I guess that Mr. W.CDavis had a bad day when he wrote the chapter...  best regarsds, Montero | |||
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Thank you this answers my question  | |||
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Alf
The question was whether weight affects wind drift and the answer remains no. The answer is within the very quote you use to seemingly prove the opposite.
BC is a factor in wind drift. Weight is a factor in BC only in the sense that you take note of what it is, in order to do the math. Increasing weight does not neccesarily increase BC but you know that. You can have bullets of the same weight and calibre with differing BCs and the highest BC will produce the lowest drift, if speed is the same and you know that too. You can have a 95gr bullet with a BC almost double that of a 500gr .458" bullet. Launch both at the same speed and the 500gr bullet will lose the wind drift race every time. Why are we arguing over something as elementary as this?  | |||
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I propose a toast to that one!  If yuro'e corseseyd and dsyelixc can you siltl raed oaky? | |||
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Burp !  I ain't turning down any free beer! | |||
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Almost sounds like a "chicken or egg" argument. Seems to me though, that adding weight to a bullet only lessens drift if it increases the BC. Therefore, BC comes first, and bullet mass is only a factor insofar as it influences BC. If you improve BC without changing weight (ie. longer monometal bullets), weight cannot be a factor in the difference in wind drift. N'est pas? Cheers, Canuck | |||
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Canuck, Of course you are right. One can reduce weight and reduce wind drift. One can also increase weight and reduce wind drift. One can have two bullets of differing weight that have the same wind drift values. One can have two bullets of the same weight with differing wind drift values. Logically one could say that if a bullet has weight, it will have wind drift. By the same logic, a weightless bullet will have no wind drift.  | |||
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I have followed this discussion with interest because I had the same experience that 416Rigby had this past weekend. I had previously tested a 260gr Partition in my 375HH, and it appeared to be just what the doctor ordered for a long range antelope round. I loaded up 10 rounds to confirm my initial data, and fired two, five round groups at 100 yds. I got four groups; two on each target. When superimposed on one another, four rounds were three inches high and about an inch right, and the six were 2.2" further right and approximately an inch lower. The wind was probably a steady 10mph, with gust up to 25-30mph, coming left to right at not quite 90 degrees to the line of bullet flight. The bullets behaved just as predicted above. The problem was not my rest, the rifle, or the load, but the wind. Like Mike416Rigby, I would not have thought that I would have gotten that much movement in 100 yds. Thanks for your interesting, informative discussion. You can argue about the fine points of this and the tongue in cheek comment above from Gerard is suitable for bronzing, but the fact of the matter is, if you are shooting in the wind, it is going to move the bullet around-a lot! And it increases with distance geometrically. About 1"/10mph@100; 3"/10mph@200; and 7"/10mph@300 according to my ballistic program. That's some serious hold off in a 25mph wind. Thanks again for reminding us all how important wind doping is. Kudude | |||
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