ok, i get it that the barrel of the rifle is pointing slightly upwords relativly to the sights. my several questions are: 1. why? 2. who invented this & when? 3. do all modern rifles shoot in parabolic trajectories, since when?
It was invented by whoever created the universe. It’s just gravity that makes a bullet fly in a parabolic arc. It’s not just bullets either. Anything that isn’t self propelled is going to fly in a parabolic arc.
The parabolic arc assumes there are no effects from aerodynamics, which isn’t always true. Baseballs can curve, for example, and so can bullets. (ETA) Bullets however tend to fly in a spiral pattern rather than a baseball style curve, just because the bullet is spinning around like a football as it goes through the air.
yes, but sombody thought it would be wise to put the barrel slightly upwords, which makes the bullet fly up and then down. if the barrel would have pointed straight ahead, the bullet would fly in a parabolic course downwords only!
That was done as soon as they started putting sights on guns. Most smooth bore muskets didn’t have sights. A smooth bore musket always fires curve balls. Once you get past about 50 to 75 yards, you don’t know which way it is going. Many smooth bore muskets had the bayonet lug on top and you could kinda use that as a sight if you wanted to, not that it helped much.
When they first started making rifles (back in the flintlock days) they realized that the sights were only good for a certain range. Some rifles and rifled muskets just had a simple fixed sight, typically set for something like 100 yards. Some had leaf sights where you’d flip up a little leaf for 300 or 500 yards. Some rifles had some pretty darn fancy adjustable sights. They had the sights figured out even when the weapons themselves were still fairly crude.
The rule during the civil war (when muskets started to regularly have sights) was to aim for their belly button when they got close. That way, since you’d end up shooting a bit high (due to the arc), you’d still hit them somewhere in the chest.
Isn’t this a simple way of ensuring that you will always miss? You aim on the level, the bullet drops below the level you aim. You miss.
You work out how much the bullet will drop over the distance you fire, you point the sights down that same angle, automatically the barrel rises the same amount when you aim. Pull trigger, bullet exits barrel, hits target. Turns out the trajectory was a parabola. As above., It can’t be anything other than a parabola because there is constant downward acceleration by gravity through the entire flight.
Strictly speaking, it’s rarely true - unless the gun is fired in a vacuum, atmospheric drag will distort the parabola.
You could say this concept was invented when primitive hominids learned how to throw rocks. If you want to hit an animal even a few paces from you, the rock must start out heading toward a point well above the animal. The case for a gun is exactly the same - though the higher velocity calls for a smaller vertical correction.
If you want to see the arc, grab the end of your garden hose and turn on the water.
Isn’t it more accurate to say , rather than the barrel pointing up a bit, that the sights point down a bit?
The sights point down relative to the axis of the barrel. The barrel points up relative to the line of sight to the target.
I’d say these two ways of describing it are of about the same accuracy.
Your sights are on target. The barrel is angled up. The bullet is lobbed to hit the target.
All projectiles (or, rather, all that are under the influence of a body’s, such as the Earth’s, gravity, and that do not go into orbit) travel in a parabola. This fact was discovered by Galileo Galilei, through his experiments with rolling balls down inclined planes. It was initially applied to calculating trajectories of cannonballs and the proper aiming of cannons, but it works for rifles too.
When forces in addition to gravity are at work, the trajectory may not be parabolic.
All scientific laws (except, perhaps, a tiny handful of absolutely fundamental ones) apply only ceteris paribus. Do we really have to spell that out explicitly every time? It makes discussion terribly tedious.
This is what’s going on. Notice the optical scope that you’re looking through is horizontal and pointed directly at the center of the target. The barrel is pointed up.
When the bullet leaves the muzzle,
- The bullet is below the line of sight.
- The bullet ascends.
- While ascending, the bullet intersects the line of sight close to the muzzle.
- The bullet is still ascending and is now above the line of sight.
- Still above the line of sight, the bullet reaches an apex.
- Still above the line of sight, the bullet starts to descend.
- While descending, the bullet (again) intersects the sight axis. If the gun is properly “zeroed”, this will occur precisely at the center of the target.
- Bullet hits target. (If there is no target for the bullet to hit, the bullet will simply descend below the line of sight and continue descending until it hits the ground.)
When you adjust the elevation of your sights, you are really adjusting the angle of the barrel (relative to horizontal or the line of sight).
I agree: We shouldn’t have to point to the notion of ceteris paribus for scientific discussions, especially in the abstract. However, it really needs to be pointed out for discussions of economics, because every time an undergraduate takes econ 101 and learns about the “law” of supply and demand, he goes around spouting it off with regard to everything, completely ignoring that it’s heavily predicated on ceteris paribus.[/digression]
Sorry to be tedious. But the truth is that a typical bullet’s trajectory is very far from parabolic.
A truly parabolic trajectory would happen if the horizontal velocity of the bullet stayed constant once it left the muzzle and the vertical velocity were influenced only by gravity. In fact, a bullet quickly loses a lot of velocity to drag. Here are some numbers for a typical .308 load with a muzzle velocity of 2600 fps:
200 yds - 0.25 sec - 87% of original velocity
400 yds - 0.53 sec - 75%
600 yds - 0.86 sec - 64%
800 yds - 1.25 sec - 55%
1000 yds - 1.70 sec - 47%
Saying that “the barrel” is pointing up seems odd. It is the entire rifle. If the barrel were pointing up relative to the chamber then there would be serious problems.
FWIW Many Airsoft rifles (something like a modern BB gun using plastic BB’s) use a ‘hop’ mechanism that puts a backwards spin on the projectile that somewhat compensates for the parabolic arc and can straighten out the flight quite a bit.
Well, right - the barrel, chamber, stock, etc. are all tied together. But when talking about piece components, it is the angle/direction of the barrel that determines the initial angle/direction of the bullet, hence the reason for simply referring to the barrel.