parabolic bullet drop charts

They don't magically rise up, but if you angle the barrel a little bit towards the sky instead of just leveling it it with the surface of the earth, the bullet will first rise and then drop.

edit: the way you're thinking makes sense if you have a the rifle zeroed at zero yards. It's the same with artillery shells and soccer balls. They all "only drop", but if you angle their trajectory slightly they'll go upwards first.

Check this one out. It's from wikipedia, and I think it'll straighten your head out. The green line is the line of sight. Notice how the trajectory crosses it twice? once really close, and once farther away. Imagine that's your 50 and 200 yard zero.

mainecoon said:

I have a problem with bullet drop charts that show the round going up and then coming back down like a piece of artillery. As far as I know, bullets only drop, they don't magically rise up. This also gets into the 50-200 yard zero: are we to assume the bullet is rising at 50 and then dropping at 200? Doesn't make sense.

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Artillery shells don't either, they are propelled towards the sky and gravity begins to overcome that path and bring them back down. A rifle bullet is the same, as the above illustration shows, just not as extreme of an arch.

Bullets "rise" because the shooter actually aims them slightly "up" to accomodate the fact that gravity eventually wins. *
The longer the range, the more "up" is req'd at the start.




* Actually, gravity begins to win immediately against upward velocity, but that requires F=mg being introduced .... and that's a topic for a later date.

The diagram above shows the why of it. For that diagram the distance the scope is mounted above the bore axis will produce a larger anglular difference. But even close mounted plain iron sights will be set up the same but with a smaller angle.

By the way, the path isn't technically a parabola. The classic text diagrams for artillery or bullet flight more often shows a steadily shortening arc which is more accurate. Air resistance causes the bullet to slow down but the acceleration due to gravity is constant so as the horizontal velocity of the bullet drops with distance the arc shortens up.

mainecoon said:

I have a problem with bullet drop charts that show the round going up and then coming back down like a piece of artillery.

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Sorry to hear that. How can we help you get over your problem?

As far as I know, bullets only drop, they don't magically rise up.

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You are correct. Gravity only works in one direction. It's the same for bullets and artillery shells the drop per second vs the initial trajectory is identical.

This also gets into the 50-200 yard zero: are we to assume the bullet is rising at 50 and then dropping at 200? Doesn't make sense.

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Yes, the bullet is still rising at ~50 yards (has been rising since it left the muzzle) and falling at 200.

Mike

In virtually every case the muzzle of the barrel is going to be elevated slightly higher than the breach. It doesn't matter if you're using irons of optics. The bullet will rise above the barrel and at some point will reach it's apex and begin falling. When it crosses the line of sight the 2nd time that is the range you are zeroed.

When it crosses the line of sight the 2nd time that is the range you are zeroed....

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Wrong! "X"-Breath.
You have (by definition) two zeroes: One short range (e.g., 25 yard*) and One longer range (e.g., 225 yard*)







* (e.g, 30-06 150gr/3,000fps w/ a scope)

Only if the lobster is shooting!

Ah yes, the beginning of ballistics!

Short answer: scopes (or irons) are mounted somewhat above the barrel. While optics see in straight lines, bullets must be angled-up to meet the line of sight of the optics, and then typically arc above that line of sight and then fall below it (as the bullet experiences the "decay rate" of its aerodynamic characteristics through space). Otherwise, optics and bullet path would meet at only one distance (which is, of course, true of some optic-to-barrel alignments).

Originally Posted by mainecoon View Post
I have a problem with bullet drop charts that show the round going up and then coming back down like a piece of artillery.

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Sorry to hear that. How can we help you get over your problem?

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Thanks. But what if we replace the bullet with a lobster. Then it would not rise up.

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well those posts just made my day rfolcopter

mainecoon said:

Thanks. But what if we replace the bullet with a lobster. Then it would not rise up.

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Too early for April Fools threads.

Maine, using your theory that the bullet starts dropping as soon as it leaves the muzzle is not theory, it is fact. However unless you angle the barrel up slightly the sights will never cross paths with the bullet path, ever. then you would be forced to use a hold-over at every range from zero until the bullet hits the dirt.

And if you live in Kansas, Maine Lobsters cost too dang much to use them for ballistics trajectory testing!!

We have to use Crawdads, when we can catch a mess.

Rc

mainecoon said:

Thanks. But what if we replace the bullet with a lobster. Then it would not rise up.

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That depends on the vertical component of its initial velocity.... This is basic physics. I don't know if this is a serious question, but if it is, here goes.

Gravity is a constant, it acts on everything, all the time. The acceleration (meaning rate of change) of gravity is 9.8m/s^2. Every projectile, be it a bullet, a lobster, or a ball, has a vertical and horizontal component to its velocity. I.E., it's moving horizontally at a particular velocity, and it's moving vertically at another velocity. Gravity is always acting on the vertical component of its velocity, changing it by 9.8 meters per second, every second. It's important to note that velocity is directional. A vertical velocity of 1m/s means it's moving up, a vertical velocity of -1m/s means it's moving down. The rate of change due to gravity is constant (ignoring air resistance).

Imagine this...

You have a perfectly flat table, and you gently push a ball until it rolls off the edge. Does it rise any before it begins falling? No. Now lets say you sling the ball off the table as hard as you can... now does it start rising before it begins falling? Of course not, as the vertical component of the ball's velocity began at 0m/s, and since gravity is pushing it down at a rate of 9.8m/s, every second, the vertical velocity of the ball will only go into the negative.

Now, if you angle the table upwards so the ball starts at the low end and leaves the table at the elevated end, you will get a positive vertical velocity. That means that the ball will, in fact, rise for a short time while gravity reduces its vertical velocity to zero, and it begins to fall.

The same is true for bullets... or lobsters... When launched from a barrel, if the barrel were perfectly level, they would immediately drop below your line of sight. This makes it hard to shoot something far away. However, because we (subtly) angle the barrel upward, and in turn increase the vertical velocity, they will rise in the time that it takes gravity to decrease the vertical velocity to zero, and then it will start falling.

So when you see a chart that, for instance, shows a bullet rising up through the line of sight at 25 yards, hitting a peak, and then dropping back down through the line of sight at 200 yards, that's because the barrel is angled up. Gravity never stops, the bullet doesn't magically rise, the barrel is simply angled up.

mainecoon said:

Thanks. But what if we replace the bullet with a lobster. Then it would not rise up.

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Laughed so hard I almost chitin my pants!

I suspect the butter serves as a bore lubrication.

Mike

Ballistic testing with Crawdads and slingshots would be interesting.. I am not sure it would be PETA approved (unless it was People for the Eating of Tasty Animals).