Gentlemen,

I am new to the world of hunting, and firearms. But hope to be smart enough to persue my interest further without getting too far in over my head, and becoming discouraged. So from time to time I will post questions on varied boards, in hopes of gaining answers from the hands on experts, as opposed to trying to decipher the info in some of the long and extremely technical manuals. That said I would like to pose the following question:

On a television show this evening, it was stated that a bullet does not travel from the barrel to it's mark in a straight line, rather it arcs at some point. Is this true ? If so could someone please explain the why and how of this happening ?

Thanks,

Lynn D

P.S. Please excuse me if I have posted this question in the wrong board, but I kind of figured this might be the place

[ 11-19-2002, 10:23: Message edited by: Lynn D ]

Lynn,

A good question. The simple answer is that the bullet drops because of gravity. Faster bullets "shoot flatter" because they spend less time en route than something slower, not because they are held up by some levitating force. This is the "trajectory" that people talk about.

In theory, if you were to shoot a bullet out of a, say, 7mm Magnum, and a bullet out of a 22 short, and drop a marble all in the same nanosecond, they would all hit the ground at the same time if they were all the same height when they were fired or dropped.

A bullet is constantly falling while in flight. When "sighted in", the axis of the rifle and the scope are not parallel. The bore of the rifle is actually pointed upwards. The two lines intersect several yards in front of the rifle.

The bullet's path intersects the line of sight, say 25 yards downrange as it "climbs" upwards and then again as goes downwards, wherever the operator has determined where he/she has "sighted in" their rifle.

The relationship between scope and rifle is quite exaggerated, and therefore easier to visualize, on the real long range rigs where the rear scope mount is much taller than the front mount in an effort to get the elevation on the barrel needed for long range shooting. Holding the scope level, as would be done while shooting, one can see the upwards "tilt" of the barrel.

Tim

Lynn D---

Gravity acts on everything equally. A bullet leaving a barrel that's perfectly horizonal will hit the ground at the exact same time an a bullet dropped on the ground from the same height.

The only time a bullet travels a straight line is when it's shot towards the center of the earth.

To complicate matters some, wind blows bullets of course, too. Marksmanship involves calculating how far above of below the line of sight the bullet will be at the range you're shooting and the amount the wind has blown it off course. The line of sight is straight, the bullet's path is always curved....and that curve gets steeper as the range increases.

Go HERE and download a ballistics program that plots the bullets flight on a graph. By inputting different cartridges you can see the differences between bullet types and velocities.

Don't feel bad. Hollyweird hasn't figured any of this stuff out yet and regularly lie about it.

"The only time a bullet travels a straight line is when it's shot towards the center of the earth." -- or directly away from same, discounting the effects of the Earth's rotation, if fired from somewhere besides one of the poles.

Lynn D.: The only dumb question is the question which isn't asked. Ask away here on AR and you'll get lots of answers -- and some of them, like these, will even be right! You'll be able to sort out the wheat from the chaff.

Many factors act on a projectile in motion (bullet). For instance the rifling in your barrel causes the bullet to spin in a clockwise direction. This causes the bullet to wander towards the right over longer ranges.

Low temperatures cause air to be more dense and gun powder to burn differently, so a given load (bullet/powder/primer combo) will fly slower in winter than in summer. This is more than just a theoretical issue. A load worked up in a Canadian winter that is high pressure and high velocity in your rifle, might be dangerously over pressure if you use it in summer. The additional environmental heat can cause unsafe temperatures and internal pressures after the rifle fires but before the bullet exits the barrel.

As you look over your barrel there are actually three "lines" that interact: sight, bore and bullet. The line of sight is a straight line from your eye to the target. The bore line is a straight line that goes down the centre of your bore straight out into space. The bullet line is the actual path of the bullet through the atmosphere.

Many pictographs show the bullet as travelling up and then down in a constant curve. This is a good example, but technically incorrect. The bullet starts up the bore line and goes straight as long as it is in the bore (barrel), about 3-8 milliseconds. The moment it leaves the bore it starts to drop. The drop is caused by good old fashioned gravity. As other guys have said, it drops vertically at the same time as it is propelled forward. Because the bullet slows down as it flies (air friction), the "curve" of the drop is steeper the further the bullet flies. The speed of drop is the same speed as any other falling object - 32 ft per second per second, or 32 feet squared per second. If you are lucky, the point comes down range when the target, your line of sight and the bullet path intersect. If that happens, you've hit the target. Many things can interfere with a hit: wind, twigs, optical illusions that cause you to not shoot straight at the target, estimating the distance incorrectly and shooting over or under the proper range (distance) are but a few. Ballistic engineers dealing with artillery shells, which fly for miles and are in flight for a lengthy period, even have to calculate for the earth's spin while the projectile is in flight. As is said by ballisticians, in physics there is no such thing as a free lunch.

Some non-shooters point at a shooter with a scoped rifle and say "unfair." Hardly. Let them try it. Amongst other things, the older a person gets the more difficult it is to focus his/her eyes. Iron sights want you to focus on three things at once: rear sight, front sight and target. Young eyes adapt by shifting back and forth with the speed and dexterity of youth. A scope permits older eyes to just focus on the sight and target. It levels the playing field, so to speak, and permits more accurate gereatric shooting ( ). Wounded critters are bad form - very undesireable.

[ 11-20-2002, 20:23: Message edited by: BBBruce ]

Actually, an object falls 16 feet in the first second and accellerates its fall at 32 feet per second each second thereafter -- in a vacuum. Free fall is, of course, somewhat slower in atmosphere and varies according to the density (and air resistance) of the falling object. All of this is too approximate to attempt to apply with any accuracy to a continually slowing bullet describing a parabolic arc, so just rely on Capt. Ingall's tables for a close approximation of trajectory.

The bullet will travel in an arc in relationship to the gun's sights. In other words, for the sights to be at the same spot the bullet will hit, they have to intersect. Therefore, the bullets trajectory (imagine a straight line from the bore of the rifle for simplicities sake), will be slightly angled upwards, in comparison to an imaginary line drawn through the sights/scope which would be slightly angled downwards. These two imaginary lines cross twice, as the bullet leaves the bore and when the bullet gradually drops towards the earth. Man I wish I could draw on here. Ok try this. You have a man, right Lynn? And you live in Quebec, so you should have snow by now. Have your man go out back and wiz in the snow. You'll notice that when his weapon is perpendicular to the earth the trajectory is just straight out and then falls to the snow. When he aims at a slight upward angle, it seems as if there is an arc. The bullet will work the same way. See, trajectory 101, feel free to try this at home. Just don't get arrested. - Dan

Think of the path of the ball when a pitcher makes his delivery. Think of slow pitch softball and a 98mph fastball in baseball. Big difference. Bullets act the same way in flight, to a much lesser degree, of course. Don't mean to over simplify, but that's what happens when things fly through the air.

These claims about a dropped marble, a relatively slow .22 rimfire bullet, and a high velocity bullet all hitting the ground at the same time if fired parallel to the ground from exactly the same height and fired (released) at exactly the same time are accurate, provided you make a few more assumptions: You have to assume that the ground is exactly flat and smooth, without curvature, and you have to asume that there's no effect of air on the projectiles to alter their course or alter their descent velocity (i.e., the speed with which they move toward the earth because of the effect of gravity).

But the earth is actually curved. If you could fire the bullet parallel to the ground at a high enough velocity, and if there were no air to slow it down, its downward curve (because of the effect of gravity pulling it downward toward the earth) could conform to the curvature of the earth, meaning that it would go into a permanent orbit around the earth. And that is exactly what happens with earth satellites, whether natural (like the moon) or man-made (like the Hubble telescope, and hundreds of others).

[ 11-20-2002, 07:08: Message edited by: LE270 ]

I always wondered how you Canucks calculated trajectories. Now I know, the same way as you write your names.

LynnD,
You haven't reposted, so I must assume you have not understood it (otherwise, you'd have said, "I see, thank you, all, for your lucid explanations.) First, don't be concerned if you haven't understood all of this, some of it really is very esoteric stuff and has little to do with hitting something with a firearm, bow or catapult, (or everything to do with it if one is really technical.)

JBelk's explanation started out real well, and I thought he was gonna' nail it, but he drifted off a little. Netim gave a good explanation of the "how" part with his discussion of line of sight/axis of bore relationship which follows from JBelk's discussion. The other comments really relate to the discussion of the principle of physics which simple put states that the force of gravity is a constant. That is to say, all objects fall at the same rate regardless of their mass in a vacuum. However, no one has really answered your first question. I'll try.

Because gravity causes a bullet to start dropping the instant it leaves the barrel, in order to hit a target any distance from the barrel, you have to point the rifle up to compensate for the bullet's drop between the barrel and target. All the rest of the discussions relates to the resultant relationship between the line of sight (eye to target) and axis of the barrel (how far up you point the barrel to compensate for the bullet drop.)

We do this automatically when we throw a ball or rock at something, even real young fastballers. We did it instinctively with our BB guns where we could see the arch of the flight of the BB. With hi-velocity rifles, you cannot see the bullet's flight, so you must achieve the right amount of hold-over or super elevation by experimentation.

But, you gotta' admit, this is one knowledgeable (and sometimes esoteric)group on everything from ballistics to world politics. You gotta' a question? We gotta' an answer (or six or ten.) Ku-dude

[ 11-20-2002, 23:03: Message edited by: Ku-dude ]

You have to use a little aiming manipulation, B3 (that's what the lovely assistant is for). Of course, if yours is bent, all trajectories will be bent as well. - Dan

Dan,
You probably heard of the middle aged guy who went to see his doctor.
"Doc", he said, "20 years ago when I got up in the morning I had to use both hands to push it down so I couls pee in the toilet. Recently, I've come to notice that I can push it down easily with one hand. Does this mean I'm getting stronger?"

Kudude,
Does that mean Belks a drifter, partner!

Interresting thread, 20 people posted the same answer, well more or less...

I suspect the question'er is totally confused by now and will shortly take up jacks or ping pong..I know I am.

Belk, ever notice Hollyweird shows binoculars with two holes, as opposed to one field of view, all scopes are on takedown guns and all of them stay sighted in, all bullets make sparks when hitting metal and all cars explode when shot, they shoot pistols held sideways and all the scopes have funny crosshairs and on and on!!

OK, to confuse a little more.

I remember hearing about some Super Genius guys, who disproved the theory of two objects of different weight falling at the same speed in a vacuum. They said that the heavier object actually does fall faster. But I sure as hell can't prove it.

DLS - It's because the heavier (more massive, actually) body has more of its own gravity; therefore, the attraction between it and the earth is a tiny bit greater than the attraction between the earth and the less massive body. Einstein figured it as

F = G(m1)(m2)/r^2

G = gravitational constant
m1 = mass of one body
m2 = mass of the other body
r = distance between them

What does this have to do with the original question? Nothing, but that's never stopped me before.

[ 11-21-2002, 07:37: Message edited by: JJohnston ]

Maybe it is just me, but I was wondering how LynnD had 241 posts on this forum, but still claims to know nothing of hunting, firearms and ballistics? Just wondering!

I have a friend named Lynn - a male wif one 'o dem "penussus" Dan was talking about.

Gentlemen,

Thank you very much for your answers, I believe I understand it now

JBelk,

Have downloaded a ballistics program and plan to use (experiment) it this weekend. Thanks.

Stonecreek,

Got that question part figured out now, so look for further queries.

dan belisle,

Only a Canadian could come up with that suggestion for an experiment

Ku-dude,

I am great at hitting things, they are just not always the things I am supposed to be hitting

Atkinson,

Ping Pong, Jacks or ballistics study ? Hmmmmmm...what to do ??

JJohnston and Jerry O,

WOW! Way over my head !

Mark White,

I like the idea of being a jack of all trades and a master of none, sort of gives me room to learn
and grow. Thanks.

Lynn D

Actually, BEJ, to give credit where it is due, it was BBBruce who coined the "penus" term. Managing my own has always been challenge enough for me. - Dan

Hey Lynn, it looks like I'm going to be at AMT in Montreal in the next month or two. Any chance we could hook up for a 50 or two? - Dan

I'm sorry Lynn. Somehow I thought your post sounded like a "Troll" posting. I should have checked you other posts and noted what forums they were mainly posted onon. It just seems that there have been a lot of trolls here lately. Again sorry for thinking you were one .

efry - Lynn is definitely not a troll. She's very nice, very clever and like she said, just actually getting into the serious shooting stuff.

By an odd coincidence Bruce, it just so happens I still DO have a doe tag. However, you're reading way too much into it, I simply thought it would be interesting to meet Lynn (and I'm sure, her significant other) as long as I was in the neighbourhood, so to speak. As to my weapon, well I may not be able to touch the bottom (that's Longbob's job, apparently) but I can rub the be'jesus out of the sides. - Dan

Ray,
Re: Jack's drift, let's not interject windage into this discussion.

Lynn D,
I was "physics resistant" in school too, but reloading and shooting has taught me more about physics than anything I've done in my adult life. If you are going to understand what is going on technically, you will learn basic physics.

On a lighter note, more "Canadien" note, my wife constantly complains that I have a problem hitting what I aim at. Ku-dude

efryman,

That's okay, don't worry about it, I have been suspected of being worse than a troll

Lynn D

Lynn,

If you want to really see something neat, find someone with a .45 Automatic Colt or a revolver that fires the .45 Automatic cartridge. Find a range somewhere that has a dark background, like an earthen birm after a rainshower. Stand behind them and look at the birm while they slowly fire at the earth. Make sure the birm is 200-400 yards. You will be able to see the bullet as it leaves the barrel and flies towards the birm in a graceful arc.

Some years ago I was priveledged to go shooting with a collector of submachine guns. He had two Thompson submachine guns, one from the Virginia State Police that had never been fired and the other was from the New York State Police. That sub was his shooter. Setting the "ladder" style rear sight up to 800 yards I proceeded to use the semi-automatic setting and single fired bullets in long "slow" arcs down to a birm. It was simply astonishing. I then set it to full auto and with a 30 round magazine tapped off 3-shot bursts that would arc out and then hit the dirt; whup-whup-whup. It is a sight I will never forget.

Sometimes physics is a beautiful thing and then sometimes wonder is even better.

Drawing the image took but a moment. Getting the danged thing into AR took FOREVER, but here it is�

Sys - You could have saved yourself a lot of trouble by just telling Lynn, "Shoot high if you miss and if that don't work shoot higher yet!"

By the way, what caliber is your example rifle? It looks suspiciously like my Browning shotgun.

<just kidding>

I thought he was using slugs in a A5 too, Pecos...

Kristofer

I think you're right. Shot doesn't fly that neatly. Had to be slugs. But his data is correct, Lynn.

Lynn,

Take a look at that drawing by Sysephus, it really shows what everybody is talking about very well. The straight line is the direct line of sight normally seen through the scope; the thing to not is that the bullet crosses it twice once relatively close to the shooter and once at the point the rifle is zeroed. That first crossing point is important as it is roughly 25 yards away for most centre fire deer calibre rifles in the .243 to 30-06 range. So when fitting a new scope, if you sight it in a 25 yards first when you move back to 100 yards it will be more or less on target and just need fine adjustments. It can save a lot of time and trouble at the range!

Regards

Pete