Often in the shooting community you can hear phrases:
This caliber (at such and such distances) has a BETTER “flatness“, this one has a WORSE, etc.
But why is “FLATNESS” (the bullet trajectory that is as close to a “straight line” as possible) so important?
To avoid wasting time on long explanations, let’s get straight to the point: TIME!
The flatter the trajectory, the less TIME the bullet is in flight, which means:
Less bullet deflection by wind
Less deflection by derivation
Less influence of all atmospheric factors
Greater accuracy
Better Energy is preserved
(Greater penetrating and killing power)
Greater probability of hitting moving targets, etc., etc.
That is, all NEGATIVE factors have a LESS effect, and POSITIVE ones are preserved LONGER.
In other words: THE “FASTER” you get into the pi-ra, THE BETTER! 😉
For us, the most important factor influencing long-range shooting is WIND.
We will consider its influence here in a little more detail:
Here is the formula for “horizontal deflection of a bullet by wind” from the book by B. Litz, which is used in almost all ballistic calculators (one for all bullets and calibers – and works great!).
Wd = 17.6 × Vs × Tlag
Wd — Wind deflection (inches);
Vs — Crosswind speed (mph);
Tlag — Bullet “dwell” time (seconds).
Converting the formula to the metric system:
Wm = Vs (m/s) x Tlag
Wm — Wind deflection (in meters);
Vs (m/s) — Crosswind speed (meters per second);
Tlag — Bullet “delay” time (in seconds)
(= “true time” of bullet flight – “estimated time” of bullet flight in vacuum).
Example:
Given:
Bullet GGG SMK 190 grain, V0 = 780 m/s,
Distance: 1000 m
Wind: 8 m/s at 90° (i.e. coefficient 1)
“True time of flight” of bullet at a distance of 1000 m = 1.97 sec.
“Estimated bullet flight time in vacuum” = 1000 m / 780 m/s = 1.28 sec.
Calculation:
Tlag (delay) = 1.97 sec. – 1.28 sec. = 0.69 sec.
Wm = Vs (m/s) x Tlag = 8 m/s x 0.69 sec. = 5, 52 m (or 552 cm.)
As you can see, only the bullet’s flight time is taken into account – regardless of its mass, shape, etc. That is, again, it is TIME that plays a key role in wind deflection.
Happy hunting, Gentlemen!