Bullet rise II.
Airbornerizz,
The discussion your people are having at work is pretty misplaced. A bullet will, as tsr1965 and most of the others pointed out, tend to a) fall, b) slow down,...and therefore fall faster as it relates to distance covered by the bullet.
But, there are some slight tangibles that tend to get over exaggerated. One being spin drift, bullet climb/drift due to the aerodynamics. The other is 'Coriolis effect', or climb/movement due to the earth rotating. These are true and documented phenomena. HOWEVER, keep in mind it's so minute so as to never come close to the rate of fall a bullet normally experiences on it's travel.
Under normal time of flight at atmospheric conditions you might expect a bullet to fall 300 inches at target distance. Instead you find the bullet only fell 297 inches due to spin drift. Meaning the bullet fell and slowed down from the time it left the barrel, just 99% of what you expected it too. Coriolis effect is the same. Based on the Earth's rotation, a bullet will hit high or low. Again though, it's measured in single digit inches across thousands of yards. Yes, firing directly East the bullet might end up 4"-5" higher than where you aimed, but it still fell 360".
To clarify, in extreme long range shooting there are known adjustments to be made for what the bullet may move from it's expected trajectory. But, the bullet still falls and slows down from the very instant it leaves the barrel.
The discussion your people are having at work is pretty misplaced. A bullet will, as tsr1965 and most of the others pointed out, tend to a) fall, b) slow down,...and therefore fall faster as it relates to distance covered by the bullet.
But, there are some slight tangibles that tend to get over exaggerated. One being spin drift, bullet climb/drift due to the aerodynamics. The other is 'Coriolis effect', or climb/movement due to the earth rotating. These are true and documented phenomena. HOWEVER, keep in mind it's so minute so as to never come close to the rate of fall a bullet normally experiences on it's travel.
Under normal time of flight at atmospheric conditions you might expect a bullet to fall 300 inches at target distance. Instead you find the bullet only fell 297 inches due to spin drift. Meaning the bullet fell and slowed down from the time it left the barrel, just 99% of what you expected it too. Coriolis effect is the same. Based on the Earth's rotation, a bullet will hit high or low. Again though, it's measured in single digit inches across thousands of yards. Yes, firing directly East the bullet might end up 4"-5" higher than where you aimed, but it still fell 360".
To clarify, in extreme long range shooting there are known adjustments to be made for what the bullet may move from it's expected trajectory. But, the bullet still falls and slows down from the very instant it leaves the barrel.
0
-
Bullets typically rise when fired because the conventional bullet trajectory (by design) aims the bullet slightly upward to create a "rainbow" like arc.
The bullet, which is launched from beneath the line of sight, will go up to cross the line of sight, fly a while while going up a few inches, then fall down and recross the line of sight on its way down until it hits the ground.
Its a bit analogous to a quarterback throwing a forward pass. If he wants his football to land in the receivers arms, he has to aim it upwards a little bit to get there.
The reason bullet trajectories are created this way is to increase the effective range, and to sort of "normalize" the line of sight and the actual trajectory path.
Yes, bullets "can" fall a little bit less than the pull of gravity "should" make them, due to unusual wind conditions, rising hot air (ie "mirage"), the Magnus effect (that's where the bullet rotation acts in combination with perpendicular wind to create wing-like "lift") etc, but you're really talking minimal effect that is literally going to be undetectable the vast majority of the time.
These kind of effects are mostly of interest to people who are trying to achieve maximum accuracy over REALLY far distances and physics geeks.
The Coriolis effect, in particular (deviation of a bullet trajectory due to the earth's rotation) is more of interest to artillery shooters where bullet flight time can exceed 20 seconds and where projectile ranges may be measured in miles, rather than to individuals shooting their Glock pistols over 20 yards at the range!
Edit: Sandwarrior, I don't disagree with anything you posted above.
quote:Txs: If you were to fire a bullet on a perfectly horizontal path down a level range from - for example - exactly 5 ft. above the ground, the amount of time it takes to impact the ground downrange would be the same as if you had simply dropped that bullet at your feet from this height.
In practice, this is true.
But absolutely strictly speaking, it may not be. Again, there are various factors in play (curvature and/or rotation of the earth, Magnus effect, air movement, temperature and humidity variations changing air density, etc) that can *slightly* alter the trajectory and drop rate of a moving bullet travelling over distance (either to increase it or decrease it) compared to one just dropped by hand.
Now in practice, with any ordinary type of shot, the effect of these things is so small, that they're only even measurable at extreme ranges. But the effects aren't zero, and if you wanted to, you could probably design a series of experiments firing rounds over a long distance that would highlight some of these effects.
Edit #2: Magnus effect: http://en.wikipedia.org/wiki/Magnus_effect
0 -
Here's another yukky variable; The angle of the shot taken will also affect the amount of the bullet's drop, as the amount of drop is spread out over the linear distance of the shot (taking into account the BC, bullet velocity, prevailing winds, tangents, cosines, calculus, trigonometry, yadda yadda yadda)
This is one reason people shooting steeply upwards at or downwards at a target on a hill will often shoot high; even with a rangefinder telling the distance between the shooter and the target... [:p]0 -
The only bullet that may rise is one shot from a smooth bore gun. Not likely, however possible for it to go any direction as it is not spinning.
A Bullet fired from a sound barrel with riffling in it will not rise. Can not and never will. If the barrel has defects, then it may appear to rise. If external forces act on it then it can change directions. Still it will never rise as the question was asked. If it did rise, it would always rise and could be measured with repeatable results.
If it makes you feel better to think that in the trajectory of a bullet, it rises, then feel better. Just do not put it in writing if you ever become famous. You will mess up science with what makes you feel better.0 -
As has been pointed out several times here, gravity itself is constant and this downward pull begins the instant the bullet leaves the muzzle. The fact that this projectile is moving forward at high speed and rotating doesn't change this.
If you were to fire a bullet on a perfectly horizontal path down a level range from - for example - exactly 5 ft. above the ground, the amount of time it takes to impact the ground downrange would be the same as if you had simply dropped that bullet at your feet from this height.0 -
Beantown,
What I described is the relative movement concerning bullet to barrel only.
Yes, in the case of trajectories when using a 'line of sight' method of aiming, the bullet may cross the path of the 'line of sight' twice. That is if the trajectory is high enough.
Txs,
If it were gravity at work only, then yes the bullets would always hit at the same time. However, you must consider the two variables I described in my first post, Those may have the fired bullet hitting sooner or later than the dropped one. But, that's only at extremely extended ranges, and very minute in comparison to those ranges. And only really measurable at those ranges. For all intents and purposes though gravity acts the same on every thing that falls.
goodgunparts,
What you describe is akin to a knuckle-ball. Aerodynamic forces could make an unstable bullet of round or pointed nature fly upward. But the instability is not a guarantee that it will do that.
Riomouse911,
What you describe is the Pythagorean Theorem. You have a target 400 yds. out, but 300 yds, above you. Straightforward use of the 'right triangle' theorem would say your actual distance to the target is 500 yds. But, again, this is based on aiming.
I should have been more clear in what I was trying to address and that was specifically the bullet in relation to the line of departure from the barrel. No sighting method allowed for. Just the bullet and the barrel.0 -
Sandwarrior you got it right on all counts IMO. I think the original poster was talking about the line-of-sight drawings demonstrating bullet trajectory being the pcause of the debate on "bullet rise."
Most these usually show the upward initial angle of a bullet, the first cross over the line of sight (Which is flat, naturally), the arc, then the re-crossing of the line of sight before falling to earth.
The diagrams don't say that the initial angle of the bullet is "upward" because the gun barrel itself is angled that way to allow for the particular trajectory to meet at whatever distant point is sought.
I'm with you; bullets start to fall the second they're fired, as do footballs (or anything else) when thrown.0 -
There are only two REAL considerations when figuring bullet drop:
1. Time of flight.
2. acceleration of gravity (32 fps per sec).
All else are so trivial they do not exist for any real world calculations.
The reason some say the bullet rises is because MOST people sight in the weapons to shoot above the bore line, simply put we shoot the bullet 'up', but if the bore line is parallel (level) with the ground it will not 'rise'!
Hope this helps simplify this!!![;)]0
Please sign in to leave a comment.
Comments
7 comments