For you ballisticians.

[Boyd Allen]

I don't have a problem with deflection. I believe that it implies that the path of something that was already moving was changed, as opposed to a more strict definition of blown which might mean that the the movement was initiated by the wind.

As to precision of language, I encourage it. It is just that one needs to be clear as to what was meant by the writer or speaker before making the correction. If by blown one is simply referring to motion produced or modified by action of the wind, and no more, then a correction may not be in order. If, on the other hand, one is using the term as part of an incorrect description of the mechanism by which this takes place, it may be. In order to sort this out, a question needs to be asked.

 

[Tony Shankle]

I don't have a problem with deflection. QUOTE]

Boy, I wish I could say that! I had 5" of horizonal to my 3" of verticle today!

 

[Gene Beggs]

WHOA!!!! We got a big problem!!!

I had to read the links provided by Boyd and Toby several times to be sure what the author was really saying, but it soon became obvious; the Sierra manual is seriously in error about which way a bullet's nose points relative to a crosswind!

At first I thought he might be using a different term to express the direction of the wind but that was not the case. He expresses wind direction correctly as the direction from which it is blowing.

I'm thankful we have Toby Bradshaw involved in this thread and I hope Bryan Litz of Berger/J-4 will join in because there are serious errors in the Sierra manual that must be corrected. It will take some time to straighten it out !

Later,

Gene Beggs

 

[Boyd Allen]

About that box of bullets....

 

[tobybradshaw]

About that box of bullets....

About that email from Sierra ...

If they really mean that the bullet's nose (as opposed to the bullet's center of mass) moves right in a left-to-right crosswind, I will pay up without a whimper. Well, maybe a small whimper.

Toby Bradshaw
baywingdb@comcast.net

 

[alinwa]

Yep, that's exactly what I'm saying. The bullet is not free to just drift along sideways on its own; it is encapsulated if you will, by the airmass through which it is flying, which in this case is not moving relative to the ground, so there can be no drift.

Gene Beggs

Gene and Toby.....

Thank you for understanding my question and clearly stating what you believe to be true.

al

 

[Pete Wass]

Has the question

Why are heavier bullets deflected less than lighter bullets been answered or why are 68g 6 MM bullets sometimes deflected more than 118g 30 cal bullets?

Thanks,

Pete

 

[tobybradshaw]

Why are heavier bullets deflected less than lighter bullets been answered or why are 68g 6 MM bullets sometimes deflected more than 118g 30 cal bullets?

A BIB 118gr .30 cal has a BC of 0.32, and a typical 68gr 6mm has a BC of about 0.27. If you're shooting the .30 at 3000fps and the 6mm at 3400fps the predicted wind deflections are pretty similar out to 300yd. If you're not shooting the 6mm as fast as 3400fps, it would deflect more than the .30 shot at 3000fps.

Heavier bullets don't necessarily deflect less than lighter bullets -- it's the BC and muzzle velocity that determine wind deflection at any given crosswind velocity.

Toby Bradshaw
baywingdb@comcast.net

 

[mks]

Holy cow, Gene,

I had to read the links provided by Boyd and Toby several times to be sure what the author was really saying, but it soon became obvious; the Sierra manual is seriously in error about which way a bullet's nose points relative to a crosswind!

At first I thought he might be using a different term to express the direction of the wind but that was not the case. He expresses wind direction correctly as the direction from which it is blowing.

I'm thankful we have Toby Bradshaw involved in this thread and I hope Bryan Litz of Berger/J-4 will join in because there are serious errors in the Sierra manual that must be corrected. It will take some time to straighten it out !

Later,

Gene Beggs

you are right, it appears they are confusing drift due to yaw of repose with crosswind deflection. Sierra's explanation fits for the rightward yaw and drift of a right hand spinning bullet due to an upward lift force, but this effect occurs in the absence of crosswind.

Their table of crossrange and vertical deflection is also wrong. Aerodynamic jump is upward for a R-L wind and downward for a L-R wind for right hand twist.

What a mess Boyd dug up.

Cheers,
Keith

 

[Pete Wass]

My reason for asking

A BIB 118gr .30 cal has a BC of 0.32, and a typical 68gr 6mm has a BC of about 0.27. If you're shooting the .30 at 3000fps and the 6mm at 3400fps the predicted wind deflections are pretty similar out to 300yd. If you're not shooting the 6mm as fast as 3400fps, it would deflect more than the .30 shot at 3000fps.

Heavier bullets don't necessarily deflect less than lighter bullets -- it's the BC and muzzle velocity that determine wind deflection at any given crosswind velocity.

Toby Bradshaw
baywingdb@comcast.net

is having competed against 6 mm rifles, on very windy days I believe I see the 30's being more wind resistent than the 6's. There are days when they are clearly better than the 30's but where I compete most of the time, the 30's seem to have the edge and more than just hole size. One competitor in particular has a 6 PPC Varmint Hunter rifle he can shoot the dots out on lite days but when it's windy, he is more often likely to get 9's 0r 8's. He is a very accomplished shooter with many years of competition behind him and with 6 PPC rifles.

Does what you said sort of make a case for using bullets that have a better BC, a la the boattailed 6 MM bullets?

 

[tobybradshaw]

is having competed against 6 mm rifles, on very windy days I believe I see the 30's being more wind resistent than the 6's. There are days when they are clearly better than the 30's but where I compete most of the time, the 30's seem to have the edge and more than just hole size. One competitor in particular has a 6 PPC Varmint Hunter rifle he can shoot the dots out on lite days but when it's windy, he is more often likely to get 9's 0r 8's. He is a very accomplished shooter with many years of competition behind him and with 6 PPC rifles.

There's a lot more to shooting Xs than the physics of bullet flight. Knowing where to put the crosshairs (and/or when to pull the trigger) when the wind is blowing matters more than a few points of BC or a few fps of muzzle velocity. At 300yd a 10mph crosswind moves a typical 6PPC bullet sideways by 9 INCHES. A 2mph let-up (to 8mph) will move the bullet 2 rings.

Toby Bradshaw
baywingdb@comcast.net

 

[tobybradshaw]

What a mess Boyd dug up.

Cheers,
Keith

OK, now that Keith has looked into the details I won't make Boyd get an official email from Sierra. "Experts" apparently do disagree.

Boyd, send me your mailing address, and if you have a good recipe for crow, send that along, too.

Toby Bradshaw
baywingdb@comcast.net

 

[tobybradshaw]

Does what you said sort of make a case for using bullets that have a better BC, a la the boattailed 6 MM bullets?

If the BT and the FB both shoot as well in your rifle, the BT will be more forgiving if your wind reading is a bit off. But from my perspective (usually) near the bottom of the standings, the top shooters work to get a really accurate rifle and then use the wind flags and sighter target to put the record shots into one hole or on the dot. They practice so that their wind reading is seldom "a bit off."

No doubt the long range shooters who can't see their bullet holes will have a different perspective on this.

Toby Bradshaw
baywingdb@comcast.net

 

[alinwa]

A spin-stabilized bullet (like an airplane) can't be drifting sideways in the air mass and still have its nose pointed straight ahead, because .......



Toby Bradshaw
baywingdb@comcast.net

I just need to make sure Toby....... What you're saying is that a bullet which experiences a "push" let's say the previously mentioned "crosswind between 500-600yds" will drag be dragged over (downwind) but then will continue parallel to its original course.


right?


You ARE in full agreement with Gene regarding 'encapsulation' etc?


al

 

[tobybradshaw]

I just need to make sure Toby....... What you're saying is that a bullet which experiences a "push" let's say the previously mentioned "crosswind between 500-600yds" will drag be dragged over (downwind) but then will continue parallel to its original course.

Yes. Except for very brief periods when the bullet transitions from one relative wind direction to another, the bullet (or any other aerodynamically stable object) flies straight into the relative wind. That's what "aerodynamically stable" means -- any displacement from "nose-into-the wind" is corrected by the aerodynamic forces produced by fins or spinning.

Toby Bradshaw
baywingdb@comcast.net

 

[alinwa]

Yes. Except for very brief periods when the bullet transitions from one relative wind direction to another, the bullet (or any other aerodynamically stable object) flies straight into the relative wind. That's what "aerodynamically stable" means -- any displacement from "nose-into-the wind" is corrected by the aerodynamic forces produced by fins or spinning.

Toby Bradshaw
baywingdb@comcast.net

And you feel that "straight into the relative wind" = parallel to original flight path? The bullet can't be dragged into a new direction?

al

 

[tobybradshaw]

And you feel that "straight into the relative wind" = parallel to original flight path? The bullet can't be dragged into a new direction?

al

Dragged by what force? The bullet is always being dragged backwards by a headwind. The direction of "backwards" with respect to the ground is determined by the wind direction, velocity, and the bullet's velocity.

Toby Bradshaw
baywingdb@comcast.net

 

[alinwa]

Dragged by what force? The bullet is always being dragged backwards by a headwind. The direction of "backwards" with respect to the ground is determined by the wind direction, velocity, and the bullet's velocity.

Toby Bradshaw
baywingdb@comcast.net

The crosswind.

You are stating that a momentary crosswind doesn't have the ability to permanently alter the direction of the bullet with respect to the ground.

BTST, when the bullet is relinquished by the crosswind it HAS a side vector, what force causes it to resume its old course?



al

 

[alinwa]

My prior post is unclear.

What I mean to say is, regardless of the bullets attitude in relation to the ground, it HAS a new direction......... when the crosswind lets go of it it's already traveling in a new direction, all it's got to do is reorient it's nose and keep on flying.

In short, I think Newick's right (AND clear) and y'all's are wrong.

But that seems a common thread eh!! goes back a while.



al

 

[Pete Wass]

Something I have noticed

when changing targets and taping up backers, often bullets pass through both the target and backer in what appears to an angle downward and right. I don't ever remember seeing a hole that semed to be angling toward the left. I am thinking all the while when reading this, some of what I see on the paper would be in direct contradiction to the science. Perhaps I just don't understand what I am reading here or there are extenuating circumstances.