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Absent of air resistance, arrows will fly furthest on horizontal plain at 45 degrees angle.

Why machine gunners do not use this tactic and shoot further?

Is this because bullets have more air velocity drags?

Should this be asked at military stackexchange?

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closed as off-topic by ACuriousMind, Jon Custer, Qmechanic Sep 28 '16 at 17:02

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    $\begingroup$ Generally, the goal of firing a gun is precision, not distance. If you fire a gun into the air, the bullet will become subject to dynamical atmospheric effects that will make it nearly impossible to hit a target. $\endgroup$ – Dmitry Brant Sep 28 '16 at 2:42
  • $\begingroup$ we no longer have mass troops against mass troops? Oh better crowd control mechanism is available for splash damage like mortar. I see I see. Should be on history stackexchange. $\endgroup$ – user4951 Sep 28 '16 at 3:06
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    $\begingroup$ I'm voting to close this question as off-topic because it is not about physics. $\endgroup$ – ACuriousMind Sep 28 '16 at 12:23
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The main job of any gun is to impart energy to its targets, whether they be humans or machines.

Leaving out the question of whether or not that's a worthy mission, just recall that the kinetic energy of a moving object is $\frac{1}{2}mv^2$, where $v$ is the object's velocity vector. Bullets, unlike artillery shells or missiles, do all of their damage through this equation.

As this question tells you, assuming that you're firing the bullet roughly parallel to the ground, gravity is primarily going to contribute to a loss of accuracy, while air drag is going to decrease its energy. It's easy to make a bullet go faster with better/more propellant, so you can improve on the travel time to the point where gravity isn't a significant factor in affecting the ability to deliver a bullet over the range it is intended--human factors (in the case of a human-operated gun) become the major issue.

So we come to air drag. That question above shows that air drag increases with the square of the velocity, just as does kinetic energy. It's a force, which means that it's an acceleration: a change in velocity over time. In other words, the longer the bullet spends in the air, the more the drag will have reduced its velocity, and thus its energy.

So the general guidelines are: if you want a bullet to deliver the most energy to what it hits, and to hit the right thing, you want a bullet to go as fast as possible (high velocity load), and spend the least amount of time in the air as practicable (shortest path).

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