I don't know how much interest there is in the following, but I thought I'd offer it. Because I'm lazy and busy, I copied and pasted it from another forum where I posted it some time ago. Parts of it will sound a little out of context without the other 4 pages of posts.
The science of ballistics is so complex that I can assure you any explanation I offer will be questioned. The major problem, because of this complexity, is that no answers are adequate without using higher forms of mathematics and then 99% of the participants in a discussion of this type cross their eyes and lapse into a coma. The other danger is that if you “dumb it down” to where it “might” be understandable, there will always be someone with just enough knowledge to be dangerous, and the discussion becomes ego based. Maybe the biggest problem is I understand all of this pretty well but often do a poor job of communicating it to others.
I know this first hand because I've been involved in this subject matter more times that I can count on internet forums and I can almost guarantee there will be confusion/disagreement with very few happy endings. LOL
Anyway, because I'm aware of how this usually turns out, I doubt if I'll have the time or fortitude to continue my participation after this initial post. If you disagree or don't understand my comments here, I suggest you Google terms like “ballistic wind drift", “ballistic drag coefficients", “ballistic drag slopes", “transonic wind drift", etc. I'll also caution you to find credible links to any reference material you find and it would be best to avoid any links to internet forums because it's nearly impossible to separate the wheat from the chaff where forums are concerned.
I'm going to address a few of the points made during this thread and comment on them:
First, a couple of analogies have been made concerning air craft or boats and how they drift in a fluid medium. I'm afraid these analogies, intuitive as they may be, aren't very useful because they are not gyroscopically spin stabilized projectiles. There is never a wind component acting on the side of a spinning projectile because all gyroscopically spin stabilized projectiles “weathervane” into that wind component almost instantly and air flow is always into the longitudinal geometric axis of the projectile.
While aircraft and boats do in fact need to “weathervane” into the air or current to negate drift, the science behind it isn't appropriate for spin stabilized projectiles. Sorry, but that's the best I can do without typing another 1,000 words.
Second, and most importantly, it appears that no one recognizes one of the primary tenets of projectile wind drift. The higher the drag coefficient, or drag if you prefer, the greater the wind drift. This is why “lag time” differences in a vacuum vs atmosphere have a direct correlation to wind drift calculations.
Why is this so important? It's because we're dealing with the transonic range of velocities and the aerodynamic properties of flight with spin stabilized projectiles in this regime are almost the total opposite of supersonic velocities.
If you look at the following image (where I've added some descriptive labels that show the approximate zones and Mach numbers we're concerned with) of the data producing a drag slope from Doppler Radar testing at Lapua's facility you'll see that in the supersonic range, drag coefficients increase with lower velocities while the opposite happens in the transonic range of rimfire velocities.
In other words, transonic projectiles have less drag at lower velocities and thus less wind drift. Supersonic projectiles have less drag with higher velocities and thus less wind drift.
I'm hoping this explanation, simple as it is, will be adequate.
http://s239.photobucket.com/user/HuskerP7M8/media%20Posts/Transonic%20Wind%20Drift/Slopea_zps901b1ed2.jpg.html>
Let me also show you some of my own data of only the transonic portion of a drag slope just in case some of you don't believe round nose lead bullets behave the same as streamlined jacketed centerfire projectiles. This data was gathered in my tunnel using two highly modified chronographs with 64 Mhz clock speeds and 10 ft screen spacings at a 45 yd distance. You'll notice this portion of a drag slope is almost identical to the Doppler Radar testing from Lapua.
In case you're wondering what the red data points are indicative of, they're 4 bullets with an offset Cg that never stabilized during flight to the target and had much greater drag which produced higher numbers for velocity lost.
http://s239.photobucket.com/user/HuskerP7M8/media%20Posts/Transonic%20Wind%20Drift/Slopeb_zps6ba75a69.jpg.html>
I can also show you another portion of a test I did comparing the ballistics from a sample of three different manufacturers of 22lr bullets. In this case I also calculated a Ballistic Coefficient and the wind drift numbers.
Edit for this post: It should be obvious that calculated Ballistic Coefficients are of limited use in the Transonic range of velocities because the velocity itself is the dominant factor and not the projectile shape/form element.
The wind drift numbers were calculated using Dr. Geoffrey Kolbe's 3rd Order Polynomial Drag Function equation that Geoff derived from Robert McCoy's testing at the BRL (Ballistic Research Laboratory) at the Aberdeen Proving Grounds in 1990.
This research is titled “Memorandum Report BRL-MR-3877", if anyone wants to Google it for reading. It's the only definitive research ever conducted on 22 rf ballistics and should be required reading by everyone with an interest in the subject.
2nd edit for this post: Some of you might find ideas for experimentation if you look at BHN's and the working pressure of 22lr cartridges....just a thought and might be a dead end, but thought I'd mention it. I'm thinking complete and consistent obturation with lower pressures in conjunction with compatible chamber dimension may be one of the avenues to explore.
http://s239.photobucket.com/user/HuskerP7M8/media%20Posts/Transonic%20Wind%20Drift/Test_zps277a85be.jpg.html>
What the Heck! Here's a few pics of my ballistic set-up:
Landy
http://s239.photobucket.com/user/HuskerP7M8/media%20Posts/Transonic%20Wind%20Drift/Chronoa_zps4fd456a7.jpg.html>
http://s239.photobucket.com/user/HuskerP7M8/media%20Posts/Transonic%20Wind%20Drift/Chronob_zpsaaa39228.jpg.html>
http://s239.photobucket.com/user/HuskerP7M8/media%20Posts/Transonic%20Wind%20Drift/Chronod_zpse7054a0b.jpg.html>
http://s239.photobucket.com/user/HuskerP7M8/media%20Posts/Transonic%20Wind%20Drift/Chronoc_zps365e2b05.jpg.html>
“In God we trust; all others must bring data.” “Without data, you're just another person with an opinion.” “If you can't describe what you are doing as a process, you don't know what you're doing.” “It is not enough to do your best, you must know what to do, and then do your best.” W. Edwards Deming (October 14, 1900 - December 20, 1993)
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