Physics of shooting a rifle

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If you're asking specifically why a .30-06 bullet would cross the sight line at exactly 25 and 100 yards, I think those are just made up numbers that are in the very general ballpark. I think for a .30-06 with a 100yd zero, the first crossing of the sight line would happen closer to 50 yards than 25.
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Yes--I couldn't get my mind around the flat 30-06 trajectory hitting line of sight at those 2 distances.
 
JohnKSa said:
If you're asking specifically why a .30-06 bullet would cross the sight line at exactly 25 and 100 yards, I think those are just made up numbers that are in the very general ballpark. I think for a .30-06 with a 100yd zero, the first crossing of the sight line would happen closer to 50 yards than 25.
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With 180grain Silvertips, my .30-06 crosses at 52 yards and 100 yards.
 
Yeah the 25/100yd was something I made up. If 50/100yd is correct, the launch angle for zero is adjusted to from 6moa to 4moa. The bullet drop at 350yd will be less, and error caused by canting will be even less.

I picked 25yd because I have seen hunters checking zero at 25yd at indoor range. They probably did that for "battle sighting" out to 250yd.

-TL

Sent from my SM-N960U using Tapatalk
 
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Sorta continuation / elaboration from other thread.

I have a 40-year old Rem 700 bdl in .30-06. A Redfield wide screen 3-9x scope is on it, with duplex reticle. Clearly it is setup for hunting. I zero it at 200yd so that it shoots point-blank (battle sight) up to 250yd. I tried to use it to shoot "long range" up to say 800yd. Of course not for hunting but for being silly.

What would you do to make this setup work for distance beyond 500yd? Dialing in is not practical with the closed coin-op turrets without clicks. Hold-over? The reticle has close to none reference.

Here is a vertical dope table I made up for sake of discussion

200yd 0moa
300yd 3moa
400yd 7moa
500yd 12moa
600yd 18moa
700yd 25moa
800yd 33moa

Here is piece of information that I think is important. The reticle's center to the thick post fills the width of a letter size paper at 100yd when I set the magnification to 8x.

-TL

Sent from my SM-N960U using Tapatalk
 
coin-op turrets without clicks
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From your listing of integral MOA chart, you won't/don't need clicks
thick post fills the width of a letter size paper at 100yd
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Notwithstanding (what you describe as) an 8-minute post to calibrate known target
size against apparent range, what you will still need is a good rangefinder.
 
mehavey said:
From your listing of integral MOA chart, you won't/don't need clicks



Notwithstanding (what you describe as) an 8-minute post to calibrate known target

size against apparent range, what you will still need is a good rangefinder.
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Maybe I didn't describe clearly. Let me use 500yd as example.

The target is at 500yd. I already know that. No need for a range finder. Elevation is 12moa. Dialing the turret is not practical, inconvenient at the least. There is no clicks and the marks have faded. I simply don't know how much to turn the "screw head". Besides I am sure I can go back zero precisely afterwards. I just don't want to fumble with it.

Hold-over is perhaps the only option left. But how do I hold 12moa with the duplex reticle?

-TL

Sent from my SM-N960U using Tapatalk
 
But how do I hold 12moa with the duplex reticle?
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You give it a bouquet of flowers and say "sorry, it just wasn't meant to be" and buy a scope that has the elevation and subtensions you need. :)

I guess you could also correlate the MOA distance between posts @ a known distance and then mathematically derive for the distance hold over/under.

Or just buy a scope with the elevation and subtensions you need.
 
Buying my way out of a problem? Never. I just lectured my boy about it. I can't eat my own words :).

But seriously, I did buy a scope. But the rifle has been together with that Redfield for so long. I can't put myself to separate the old couple.

It is a SFP scope. The product of post subtension and magnification is a constant =8*8=64. I just adjust the magnification to have the subtension I need for the hold.

300yd, 3moa, 9x, hold midway to the post.
400yd, 7moa, 9x, hold to the post.
500yd, 12moa, 5x, hold to the post.
600yd, 18moa, 3.5x, hold to the post.
700yd, 25moa, 5x, hold double to the post.
800yd, 32moa, 4x, hold double to the post.

Decreasing magnification for longer distance is a bit backwards. Holding double, triple, or even quadruple, is a work around. It requires some reference points in the background, rock, tree branch, etc, or you just eyeball it. For example

800yd, 32moa, 8x, hold quadruple to post.

-TL

Sent from my SM-N960U using Tapatalk
 
Given bullet's BC and target distance, there exists optimum MV for minimum wind deflection.

I didn't realize that till I read an article on airgun pellet. The article gave brief qualitative explanations, but no analytical equations. I tried it on ballistic calculator. It is true. Wind deflection drops with increased MV till it reaches a minimum, and then it goes the other way. Speed doesn't always improve "wind bucking", BC always does.

That's interesting. I will post a link to the article later. Will dig out the Robert McCoy book too to try to derive an analytical solution.

-TL

Sent from my SM-N960U using Tapatalk
 
Wind deflection drops with increased MV till it reaches a minimum, and then it goes the other way.
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I can see it going down to a minimum value but don't get how wind deflection could increase again after that. Could you explain that in small words for those of us who aren't very technical minded??

Area for wind to push against, constant, right?
Time wind has to push against the bullet is variable with the velocity. Right??

Faster means less time of flight, so less time for wind to push, so less deflection, Right??

SO, once you reach the minimum amount of deflection, how would further reducing the time of flight by increasing velocity, increase the amount of wind deflection??

I don't get how that could happen.
 
Borrowed this from the Pilots of America forum--italics and color are added by me.
Concerning a recent thread, “Tailwind question”, I read it too quickly and misunderstood what was being asked. My bad.

But in my response, I mentioned that the phase “<wind> blowing from behind” alerted me to a possible misunderstanding of the effect of wind on an airplane in flight, one I’ve seen before. But my answer prompted a disagreement with jimhorner over whether an airplane in flight is “pushed” by a steady tailwind

Oldtimers are certainly sick of it by now, but a while back I posted a compilation of what I called “Stick and Rudder Moments”. https://www.pilotsofamerica.com/community/threads/stick-and-rudder-moments-redux.79699/ I mention that now for the benefit of newbies, and to point out why I think the mental image of wind “pushing” a plane in flight can lead to misunderstandings.

Most relevant was the thought that engine cooling can be compromised when flying with a tailwind:

"5) I’ve heard it said cowl flaps are especially useful when flying downwind, when cooling would otherwise be compromised by the tailwind. More recently, a forum poster here thought winds affected cooling in a Seneca, possibly due to cowling shape. Then he doubled down with: "On my 206 I've notice a 5-10 degree change in CHT based on a strong wind. I am not a fluid dynamics expert, so I have no idea exactly why. Perhaps a slight pressure change in the cowl as I mentioned, or slight turbulence in the relative wind, IDK.""

Another was a pilot’s assertion that his Flight Design CTLSi seemed to run out of nose down trim more quickly when flying into a headwind.

Let me first stipulate the obvious - of course a tailwind results in a higher groundspeed. The question is whether the word “push” is the best descriptor for how the "wind" makes that happens. So, basically a semantic debate.

My assertion remains that once in the air, barring gusts and shear, a plane “feels” no wind. The affects of wind - in this case the additive effect of the tailwind on groundspeed - is simply because the air mass in which the plane is moving is itself moving.

So, in my mental construct there is no “pushing” going on. There is no wind “pushing against” the plane. To a pilot, a plane doing 50kts with a 50kt tailwind will have identical flight instrument readings as the same plane doing 50kts into a 50kt headwind. Under the hood, he or she will be unable to tell which is the headwind and which is the tailwind situation - barring instruments utilizing ground or satellite references, of course. Of course, an experiment could be set up using pressure transducers on the nose, tail and sides of a plane and again, the movement of the airmass the plane is in - the “wind” - will have zero effect on those readings.

I want to thank jimhorner for his thoughtful response - #29 in the “Tailwind question” thread. He clearly outlines that the disagreement may be based on frames of reference: “Its <the wind’s> force most definitely IS pushing your plane, just not relative to the air. It is, however, providing a force which pushes you relative to the ground, and that force is real.”

(italics mine)

There are many frames of reference we could discuss. But point is that as long as we’re airmen discussing airplanes, what we should concern ourselves with is flight through the air and language that best describes said flight. I still feel references to wind “pushing” can and does lead to flawed or inappropriate mental models that can lead to the “Stick and Rudder Moments” that many pilots still fall victim to.
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Tailwind and headwind effects on aircraft doesn't seem to be well related to wind deflection (wind from the side /at an angle drifting a bullet).

Correct me if I'm wrong, but don't aircraft have to alter the positions of their control surfaces to counter the effect of wind from the side, below, or above?

A bullet can't do that.
 
44 AMP said:
I can see it going down to a minimum value but don't get how wind deflection could increase again after that. Could you explain that in small words for those of us who aren't very technical minded??



Area for wind to push against, constant, right?

Time wind has to push against the bullet is variable with the velocity. Right??



Faster means less time of flight, so less time for wind to push, so less deflection, Right??



SO, once you reach the minimum amount of deflection, how would further reducing the time of flight by increasing velocity, increase the amount of wind deflection??



I don't get how that could happen.
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Wind deflection is result of two factors; TOF and the force that pushes the projectile accelerating sideways.

TOF decreases with MV. As stated by unclenick's posts in the thread, the origin of the sideways force is the drag. The drag increases as the MV. Above certain MV, the 2nd factor becomes dominant, so the wind deflection comes back up.

This phenomenon happens with low BC projectiles. Airgun pellet has low BC (<0.05), so it is more noticeable. But I wouldn't be surprised light varmint bullets at super high MV have the issue.

-TL

Sent from my SM-N960U using Tapatalk
 
Tailwind and headwind effects on aircraft doesn't seem to be well related to wind deflection (wind from the side /at an angle drifting a bullet).

Correct me if I'm wrong, but don't aircraft have to alter the positions of their control surfaces to counter the effect of wind from the side, below, or above?

A bullet can't do that.
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Exactly--bullets don't have control surfaces (at least the ones used in conventional small arms); and the reference of wind (really the dynamic movement of airmass) "drifting" the bullet as opposed to "pushing" it is also "more" correct. Just like the pilot above observes, the difference between "pushing" and "drifting" may seem like a small question of semantics, but it can lead to a basis of faulty assumptions to further modeling. I'm not a fizzics expert but 25 year's of glider pilot experience ingrained this fundamental concept in real-world situations. Wind--or more precisely the movement of the airmass, will always have an effect on an object flying through the air, regardless of what direction vector the wind is relative to the flight path of the object. Our points of reference as shooters are mostly static ground-bound, so those effects are generally seen only as variations in elevation and windage at bullet impacts (keep in mind I'm not discounting the forces of inherent bullet stability, drag, coriolis, pressure wave etc).
 
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Bullets don't get pushed or drifted by wind. "Wind drift" is a misnomer maintained out of historical habit. It is what F. W. Mann tried unsuccessfully to demonstrate, likening the bullet's flight through air to a boat drifting downstream or a leaf tossed on the wind. But the numbers don't add up. Even a boat placed in a running stream or a leaf released by a tree don't instantly start moving at the speed of the flowing fluid they find themselves dropped into. First, the motion of the fluid exerts drag on the item in question, and that force starts overcoming it's static inertia and moving it. As it picks up speed, the difference between its speed and that of the fluid diminishes, so the drag force drops off, so the acceleration drops off, and the object's speed closes in on the fluid speed more and more gradually as it gets closer to it. This continues until any difference in the two speeds is lost in the noise and the two appear to be moving together. In the time of flight of a bullet, it can account only for a small fraction of the actual bullet deflection from its zero wind POI (as I showed by calculation for a 22 LR in the attachment to one of my earlier posts on page 3 or 4, IIRC).

At any rate, the official correct physics term is wind deflection, even though we keep calling it wind drift. The same is true of spin drift, which is actually a deflection caused by the yaw of repose slightly favoring one side in deflecting the bullet's headwind off the ogive of the bullet nose.
 
Bullets don't get pushed or drifted by wind. "Wind drift" is a misnomer maintained out of historical habit. It is what F. W. Mann tried unsuccessfully to demonstrate, likening the bullet's flight through air to a boat drifting downstream or a leaf tossed on the wind. But the numbers don't add up. Even a boat placed in a running stream or a leaf released by a tree don't instantly start moving at the speed of the flowing fluid they find themselves dropped into. First, the motion of the fluid exerts drag on the item in question, and that force starts overcoming it's static inertia and moving it. As it picks up speed, the difference between its speed and that of the fluid diminishes, so the drag force drops off, so the acceleration drops off, and the object's speed closes in on the fluid speed more and more gradually as it gets closer to it. This continues until any difference in the two speeds is lost in the noise and the two appear to be moving together. In the time of flight of a bullet, it can account only for a small fraction of the actual bullet deflection from its zero wind POI (as I showed by calculation for a 22 LR in the attachment to one of my earlier posts on page 3 or 4, IIRC).

At any rate, the official correct physics term is wind deflection, even though we keep calling it wind drift. The same is true of spin drift, which is actually a deflection caused by the yaw of repose slightly favoring one side in deflecting the bullet's headwind off the ogive of the bullet nose.
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Thank you for the reponse. I know it's irritating to put up with stubborn comments sometimes from people like me;). I think wind deflection is still a better term than "pushing" Anyway, I hereby promise to the forum I will never bring it up again.:)
 
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