lag time and bullet wind deflection

[michaelbz]

Why is lag time (the difference in time of flight between air and vacuum) used to calculate a bullet's wind deflection instead of actual time of flight?

 

[Keith Glasscock]

The bullet weather-vanes for lack of a clearer description. If the velocity stayed constant (due to thrust- i.e a rocket), the weather vane effect would result in nearly zero wind drift.

Now consider a rocket without adequate thrust to maintain velocity. The vaning would result in lessened wind drift as compared to a projectile that is coasting all the way to the target.

If we use a very slippery bullet, the wind will create less force against the bullet than it would with a blunt profile.

It comes down to the balancing of forces.

 

[BoydAllen]

Sometimes we forget that formulae and the variables they are made up of are attempts to predict what will happen in the real world. Different formulae and variables' predictive abilities can be compared to actual results. Theories aside, they use what they use because it works better than something else. You have no idea of how many ideas that various people have written on the internet to explain how they think that external ballistics work. Ultimately even many of those that work in and around the field fail to back up their "explanations" with any actual data. Mostly they are just the picture that they have in their heads. Bullets are not rockets, they are gyroscopiclly stabilized, which is much different than fins. Among reputable sources there is disagreement as to whether they turn very slightly into the wind or away from it. Even if they do, I defy you to tell which way the wind was blowing by examining a single bullet hole, with nothing to identify the point of aim. If there was much tilt, the hole would be elongated. I cannot tell you what the formula is for predicting wind drift, but I did look it up once, and you might be surprised as to what it does and does not contain. I would be really surprised if anyone reading this could give us that formula along with a detailed explanation. Even with such pervasive ignorance, including my own, we manage to do what we have to to deal with the conditions that we encounter, in much the same way that one does not need to know how an automobile works to drive one.

 

[BoydAllen]

Good job.