What causes bullet drop?
- Thread starter Pond James Pond
- Start date
No.
If there were no gravity the bullet wouldn't drop at all. If somehow there were air but no gravity the bullet would travel in a straight line until it finally stopped, floating in air.
If there were gravity but no air the bullet would drop but would still be going at muzzle velocity when it hit the ground.
Gravity. It's not just a good idea, it's the law.
Back to the basic OP question.
Notwithstanding bullets made of feathers, all bullets drop at the same rate* (rate being measured in time)
All bullets fired out of a level rifle sitting on a bench three off the ground will hit that ground in about 4/10th of a second.
Period.
If one wants to measure in terms of drop per distance traveled, that's a different problem.
How far they travel in through that fluid called air (or water, or molasses, or whatever, etc), within that 4/10ths second
is a function how quickly they slow down -- streamline bullet shape & bullet weight -- or drag vs intertia.
* Yeah, I know... not the same rate but rather the same acceleration.
...But Hey ! What's another "/t" between friends ?
Notwithstanding bullets made of feathers, all bullets drop at the same rate* (rate being measured in time)
All bullets fired out of a level rifle sitting on a bench three off the ground will hit that ground in about 4/10th of a second.
Period.
If one wants to measure in terms of drop per distance traveled, that's a different problem.
How far they travel in through that fluid called air (or water, or molasses, or whatever, etc), within that 4/10ths second
is a function how quickly they slow down -- streamline bullet shape & bullet weight -- or drag vs intertia.
* Yeah, I know... not the same rate but rather the same acceleration.
...But Hey ! What's another "/t" between friends ?
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natman said:
Again, for the purposes of the OP's original question, I think it's safe to assume gravity's a constant. Yes, gravity is what's acting on the bullet, but a bullet's ability to maintain it's velocity (i.e. it's resistance to air resistance) is what explains relative bullet drop.
This threads starting to get repetitive and into details that only muddy an answer that's already been made clear, IMO.
@Borland & mehavey: In my high school physics class, the teacher had a device which shot a marble horizontally while simultaneously dropping another marble vertically. While one marble traveled about 20 feet away, they both clattered to the floor at the same time.
The teacher also had a device which would sit inside a large bell jar and which would drop a marble and a feather at the same time. After evacuating the jar, the marble and feather would hit the bottom at the same instant. That demonstration really stuck in your mind.
Is physics even taught in high school any more? I guess it's mainly feelings, sensitivity and social justice now. But that's a different topic for another thread in a different forum.
The teacher also had a device which would sit inside a large bell jar and which would drop a marble and a feather at the same time. After evacuating the jar, the marble and feather would hit the bottom at the same instant. That demonstration really stuck in your mind.
Is physics even taught in high school any more? I guess it's mainly feelings, sensitivity and social justice now. But that's a different topic for another thread in a different forum.
Bushmaster1313
New member
As soon as bullet clears the muzzle the earth begins to rise towards the centerline of the barrel.
Happens every time.
Happens every time.
Yes, and ..no.
Each tiny little speck of rock dust is the same as the rock it came off of, BUT density is a concentration per unit volume. A cubic centimeter of rock and the same volume of rock dust in air are not the same density, despite each particle of dust being the same as the rock. IT is a mixure (dust particles and air), and has a different makeup, and density than the solid rock.
The pull of gravity is constant, (at a given distance from the center of the earth), so the pull on objects is the same. All try to fall at the same speed, because they are being pulled down by gravity at the same amount.
It is the relationship between surface area of the object, its weight and the resistance of the air it must pass through that changes the velocity different objects attain as they fall. This is where "terminal velocity" comes in.
Drop a 200lb man and a 200lb lead brick from high enough, and each, as they fall through the air, will eventually reach different terminal velocities. Both are under the same "pull", the acceleration due to gravity, but the air resistance to the falling man's greater surface area will eventually reach a balance with the pull of gravity, and the body will not fall any faster, no matter how much further it falls.
The same thing happens to the lead brick, but because the surface area is many times smaller than the man, the brick will accelerate longer before air resistance balances the acceleration due to gravity. Much longer, actually. SO the brick is moving much faster by the time it reaches its terminal velocity.
It may just be semantics, or your point of view. Mine is that everything falls at the same rate of acceleration speed (the pull of gravity), but it is a combination of weight, surface area, air resistance, and time that determines the final velocity a falling object reaches (on earth).
This is getting pretty deep. Density is mass per unit volume, and assuming that the rock is homogeneous (does not refer to rock's gender preference), any particles from the rock would have the same density as the rock. An air/rock particle mixture would have a different density, but I can make the original rock equivalent to that density, by just addng a large enough air envelope around it.
And to make things more complex, not all particles accelerate to a terminal velocity. They may be small enough that they won't fall at all. Plug colloidal dispersions or "Brownian motion" into your search engine (and no, Brownian motion has nothing to do with John Moses Browning).
And to make things more complex, not all particles accelerate to a terminal velocity. They may be small enough that they won't fall at all. Plug colloidal dispersions or "Brownian motion" into your search engine (and no, Brownian motion has nothing to do with John Moses Browning).
Sounds about right, but is only relevant if your rifle shoots 1" groups at 600 yards. For most of us if we fired 10 shots at a 600 yard target at 700' elevation, then used the same target and fired 10 more shots at 7000' elevation, you'd have a hard time seeing 2 distinct groups. Some shots would overlap on the target.
At 200-300 yards, which is about the max range for most hunters the difference is not enough to worry about. For guys who target shoot, or hunters who practice long range shooting it is not an obstacle that cannot be overcome.
It's relevant since the question I replied to was the difference in drop at 600 yds
Group size makes no difference since "drop" would be figured from the center of the group, and not from individual shots
In theory, a gun that shoots a 1" group at 100 is capable of a 6" group at 600, but the centers of the groups can still be at different elevations on the target, even if the edges overlapped
For all rifles, projectile drop is determined by gravity. Distance = 16 x the square of the time in seconds in a vacuum, but drag in the vertical direction is almost vanishingly small compared to the drag in the direction of line of flight.
What distance a projectile has dropped at a specific range is determined by time of flight to that range. The fact that velocity is always decreasing with range complicates the calculation hideously.
Velocity remaining at, and time of flight to, a given range are dependent on drag, which is dependent on air density (pressure and temperature) and ballistic coefficient, which is in turn dependent on the sectional density and the form factor (shape, basically) of the bullet. (It's also dependent upon velocity, which is why you either need a mastery of calculus or formulae which make good approximations and can make the calculus go away).
All bullets will descend (in the vertical plane) at basically the same rate, because the vertical rate of descent is so slow, the "side-on shape" of the bullet makes little difference.
All bullets begin an immediate descent under gravity from the line of bore from the moment they leave the muzzle, and never rise above it. They DO rise above the line of sight, by a degree determined by angle of elevation of the rifle barrel (determined in turn by the range you have sighted in for). Then of course they descend, meet line of sight once more, and begin to drop below it.
The more you read, the more you delve into this, the more hideously complicated it gets. And don't get me started on wind, or on shooting at a significant up or down angle. That makes my head spin.
What distance a projectile has dropped at a specific range is determined by time of flight to that range. The fact that velocity is always decreasing with range complicates the calculation hideously.
Velocity remaining at, and time of flight to, a given range are dependent on drag, which is dependent on air density (pressure and temperature) and ballistic coefficient, which is in turn dependent on the sectional density and the form factor (shape, basically) of the bullet. (It's also dependent upon velocity, which is why you either need a mastery of calculus or formulae which make good approximations and can make the calculus go away).
All bullets will descend (in the vertical plane) at basically the same rate, because the vertical rate of descent is so slow, the "side-on shape" of the bullet makes little difference.
All bullets begin an immediate descent under gravity from the line of bore from the moment they leave the muzzle, and never rise above it. They DO rise above the line of sight, by a degree determined by angle of elevation of the rifle barrel (determined in turn by the range you have sighted in for). Then of course they descend, meet line of sight once more, and begin to drop below it.
The more you read, the more you delve into this, the more hideously complicated it gets. And don't get me started on wind, or on shooting at a significant up or down angle. That makes my head spin.
Buzzard Bait
New member
It's
Delay in flight
Delay in flight
190's from my .308's need almost 5 MOA more elevation to zero at 1000 yards at 580' elevation than at 6600' with the same load and ambient temperature fired in the same barrel. There's been people who shot their rifles at the NRA 1000-yard range near Raton, NM, at 6600' elevation then used the same ammo and zeros at Camp Perry's 1000-yard line 580' above sea level and never got on paper. Their bullets hit the dirt below the target.
In my test with a 50 grain inflated balloon and a 50 grain bullet, both at ambient temperature dropped 10 feet, the bullet fell the fastest at 4980' altitude.
In my test with a 50 grain inflated balloon and a 50 grain bullet, both at ambient temperature dropped 10 feet, the bullet fell the fastest at 4980' altitude.
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tahunua001
New member
44 amp,
you essentially said in a few detailed paragraphs what I glossed over in a single sentence. thank you.
you essentially said in a few detailed paragraphs what I glossed over in a single sentence. thank you.
In both reality and common sense theory, a 1 inch group at 100 yards will open up at least 10% for each additional 100 yards of range. It's caused by the spreads of muzzle velocity, bullet BC (small spread caused by bullet unbalance) and air movement in the trajectory. And for each 100 yard range band, the percentage increases. For example, vertical shot stringing at 100 yards with a 50 fps muzzle velocity spread from a .308 Win is about 1/10th inch. At 600 yards, it's 4 to 5 inches. At 1000 yards, it's around 20 inches.
All this without bullet drop compensation. If bullets leave the muzzle on its axis upswing such that slower ones depart at higher angles, long range groups will be smaller in MOA than mid range ones.
All this without bullet drop compensation. If bullets leave the muzzle on its axis upswing such that slower ones depart at higher angles, long range groups will be smaller in MOA than mid range ones.
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James, every bullet, every object, no matter what, will drop at the rate of 32 feet per second, per second. (G) the only altering circumstances are air resistance to friction, and that is insignificant in bullets. A bullet fired downward will have a certain velocity imparted by the rifle from the moment it leaves the barrel, and it will still gain downward velocity at the rate of G/.
A rifle fired upwards will be accelerated upwards at the velocity imparted by the rifle, and downward pull at the rate of G will be pulling it downwards from the very second it leaves the barrel.
a bullet fired at an absolute level, directly perpendicular to the draw of gravity, will fall at absolutely the same rate of speed as a bullet dropped by hand. If a bullet was fired at well over a mile, at exact level, and a bullet was dropped at the very moment that the first bullet left the barrel, they would hypothetically arrive at the very same level when the bullet had traveled the full distance. This assumes absolute accuracy of the shot.
A fired bullet falls at the same rate as a dropped one.
Trajectory fluctuations are caused by only one thing. Changes of initial velocity, and the time it takes to reach target from the line of fire. A slow round drops more because it is accellerating downwards at G and it falls for a longer period of time than a super velocity round will.
Every bullet will drop 32 feet in exactly one second in earth gravity in vacuum. So will a bowling ball, a feather, or a space station.
A rifle fired upwards will be accelerated upwards at the velocity imparted by the rifle, and downward pull at the rate of G will be pulling it downwards from the very second it leaves the barrel.
a bullet fired at an absolute level, directly perpendicular to the draw of gravity, will fall at absolutely the same rate of speed as a bullet dropped by hand. If a bullet was fired at well over a mile, at exact level, and a bullet was dropped at the very moment that the first bullet left the barrel, they would hypothetically arrive at the very same level when the bullet had traveled the full distance. This assumes absolute accuracy of the shot.
A fired bullet falls at the same rate as a dropped one.
Trajectory fluctuations are caused by only one thing. Changes of initial velocity, and the time it takes to reach target from the line of fire. A slow round drops more because it is accellerating downwards at G and it falls for a longer period of time than a super velocity round will.
Every bullet will drop 32 feet in exactly one second in earth gravity in vacuum. So will a bowling ball, a feather, or a space station.
Pond James Pond
New member
Nice explanation, Briandg.
Thanks.
And if you could do a Youtube clip of dropping a space-station in a vacuum alongside a Hornady Amax, I would be particularly grateful!
Thanks.
And if you could do a Youtube clip of dropping a space-station in a vacuum alongside a Hornady Amax, I would be particularly grateful!
Bullets "Fly" just like an airfoil on an aircraft wing flies. The shape of the bullet determines exactly how aerodynamic the projectile is. Because there is a lack of continuous propulsion, it becomes a ballistic object subject to initial propulsive force. The shape, speed, atmospheric conditions and aerodynamic efficiency determines the rate at which the force of gravity pulls it towards the center of the earth as it decelerates.