Okay, I see. I'll definitely will try it out then, though not at 10000. Maybe 4000~.
Default speed is 1750 according to FNVEdit, so you're close.
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Gonna start working on ammunition effects now. I kinda want to C and P the info from the Wiki but I would rather just find out myself.
Once an projectile leaves the muzzle of the gun, gravity will begin to pull it down (gravity pulls it down before, too, of course, but the barrel tends to be in the way).
So assuming a simple horizontal flight path (and frictionless vacuum ), the time it takes to fall to the ground depends only on the strength of the gravitational force.
How far a projectile will fly depends on the horizontal component of its velocity.
If you increase (horizontal) velocity of the projectile, it will travel a greater distance before hitting the ground.
If you add a tilt (vertical component) to it, it gets a bit more complicated, but the basics stay the same.
For further reading see e.g. http://www.regentsprep.org/Regents/physics/phys06/amonkdrop/default.htm
Now I feel stupid when I learned that this year in school. Thanks for reminding me though. More or less has to do with the horizontal component remaining the same while gravity pushes down on the object, which simulates the downwards arc you get on an object firing straight.