Question about Projectile Motion

[random_soldier1337]

If a gun is aimed while the barrel is perfectly parallel to the ground and the ground itself is perfectly even, then how is it that the bullet lands where the tiny bit on top of the gun was pointing?

[swansont]

If a gun is aimed while the barrel is perfectly parallel to the ground and the ground itself is perfectly even, then how is it that the bullet lands where the tiny bit on top of the gun was pointing?

 

 

It doesn't, unless you've specifically sighted in the gun that way.

[zztop]

If a gun is aimed while the barrel is perfectly parallel to the ground and the ground itself is perfectly even, then how is it that the bullet lands where the tiny bit on top of the gun was pointing?

If you ever shot at targets you would know that, in order to hit the bull's eye, you must align the sight with the bottom of the black circle. This means that guns come sighted such that they point slightly upward, just enough to counter the gravitational pull on the bullets.

[imatfaal]

I presume from the above that rifles have their scope set up with the view angled downwards to a miniscule extent - or is it an an adjustment the markman can make? A quick think about it with g being 10m/s^2 and a projectile speed of 1000 m/s shows that some compensation must be made; whether this is in the view and choice by the firer or the set up of the scope is outside my knowledge

[Phi for All]

I presume from the above that rifles have their scope set up with the view angled downwards to a miniscule extent - or is it an an adjustment the markman can make? A quick think about it with g being 10m/s^2 and a projectile speed of 1000 m/s shows that some compensation must be made; whether this is in the view and choice by the firer or the set up of the scope is outside my knowledge

 

It doesn't sound like he has a scope. I'm betting "the tiny bit on the top of the gun" is the front sight, the fixed fin on the tip of the barrel. You calibrate that with the rear sight, typically somewhere between your trigger and your forward hand. The rear sight can go up and down, or side to side for windage.

[imatfaal]

 

It doesn't sound like he has a scope. I'm betting "the tiny bit on the top of the gun" is the front sight, the fixed fin on the tip of the barrel. You calibrate that with the rear sight, typically somewhere between your trigger and your forward hand. The rear sight can go up and down, or side to side for windage.

 

Yeah - that's kinda what I meant was getting mixed up with scope and sight. I cherish my ignorance in matters of the reality of firearms; I think I am the first in about 5 generations of my family that didn't need to know

[Phi for All]

 

Yeah - that's kinda what I meant was getting mixed up with scope and sight. I cherish my ignorance in matters of the reality of firearms; I think I am the first in about 5 generations of my family that didn't need to know

 

I went the opposite. I learned enough about guns to know I enjoyed being accurate with one, which made me realize I never wanted to use one to kill anything.

 

 

 

I thought this topic was going to be about firing a rifle parallel to the ground, while simultaneously dropping a bullet straight down from the same height, asking whether they hit at the same time or not.

[zztop]

 

Yeah - that's kinda what I meant was getting mixed up with scope and sight. I cherish my ignorance in matters of the reality of firearms; I think I am the first in about 5 generations of my family that didn't need to know

There are TWO sights: the rear one (also called elevator) , closer to the shooter and the front one (on top of the nozzle). They need to be aligned (by eye) and the resultant line needs to be aligned with the bottom of the dark disk on the target. This type of alignment is necessary in order to hit the target in the center, since the rifles come calibrated this way.

[random_soldier1337]

If you ever shot at targets you would know that, in order to hit the bull's eye, you must align the sight with the bottom of the black circle. This means that guns come sighted such that they point slightly upward, just enough to counter the gravitational pull on the bullets.

 

That sounds like doing more than necessary. If the gun is sighted such that while aiming it points slightly upwards, then why do you need to aim a little below target? Why not just directly at it if the gun is already sighted to compensate the gravitational pull?

 

 

It doesn't sound like he has a scope. I'm betting "the tiny bit on the top of the gun" is the front sight, the fixed fin on the tip of the barrel. You calibrate that with the rear sight, typically somewhere between your trigger and your forward hand. The rear sight can go up and down, or side to side for windage.

 

I don't actually know anything about guns. The little bit that I do know comes from video games and that isn't reliable at all. Look, for the sake of simplifying the explanation, let's just take one of the very first hand guns such as a revolver, the likes of which were used during the time of the cowboys. No fancy scopes or adjustments, just the gun and the marksman. What about these?

 

Then once an explanation is made for a simple, old time, revolver, can you guys please try to explain how a modern high tech sniper rifle would/does work? From the sounds of all the calibration that goes on and from what I heard elsewhere, a marksman needs to adjust the sights and what not while thinking of the various factors that could affect the trajectory of the bullet. Also from google, apparently some of the adjustments need to be made by a gunsmith and can't be made by the shooter in the middle of the field. For the purpose of this explanation, lets also say that a soldier given the top of the line sniper rifle is in the middle of a combat situation and is trying to get as many kills without getting killed himself (hopefully he is at least taking potshots from a good hidey-hole). Now what with all the calibration that needs to be done, how is he supposed to fare in such a situation? He has to shoot over a varying number of long distances for which, from what I understand so far, he may or may not have to make calibrations. How is he supposed to quickly and efficiently go about taking accurate shots?

[Phi for All]

That sounds like doing more than necessary. If the gun is sighted such that while aiming it points slightly upwards, then why do you need to aim a little below target? Why not just directly at it if the gun is already sighted to compensate the gravitational pull?

Aiming below the target sounds like a compensation for the kick of the rifle. A rifle will be sighted to the distance the shooter wants. If I've sighted my rifle to 200 meters, that means a target 200 meters away shows up perfectly in the sights or scope. If I know for sure the range is closer or farther, I could adjust my sights if I have the time, or I can compensate visually on the fly by aiming a little higher for farther away, or a little below for closer. Moving targets don't always move into the range you've sighted for.

 

I don't actually know anything about guns. The little bit that I do know comes from video games and that isn't reliable at all. Look, for the sake of simplifying the explanation, let's just take one of the very first hand guns such as a revolver, the likes of which were used during the time of the cowboys. No fancy scopes or adjustments, just the gun and the marksman. What about these?

Since a revolver is so short, lining up the front sight with the back has a huge margin of error. Hand guns are typically sighted straight on level to about 10m, and the old western revolvers, if they had a rear sight at all, couldn't adjust it for elevated shots. It was only adjustable side to side. If you wanted to shoot something farther away, you aimed high based on experience. If you were shooting at a moving target, "leading" the shot, or aiming ahead of the moving target, ensures the bullet hits the place the target will be in a second.

 

Then once an explanation is made for a simple, old time, revolver, can you guys please try to explain how a modern high tech sniper rifle would/does work? From the sounds of all the calibration that goes on and from what I heard elsewhere, a marksman needs to adjust the sights and what not while thinking of the various factors that could affect the trajectory of the bullet. Also from google, apparently some of the adjustments need to be made by a gunsmith and can't be made by the shooter in the middle of the field. For the purpose of this explanation, lets also say that a soldier given the top of the line sniper rifle is in the middle of a combat situation and is trying to get as many kills without getting killed himself (hopefully he is at least taking potshots from a good hidey-hole). Now what with all the calibration that needs to be done, how is he supposed to fare in such a situation? He has to shoot over a varying number of long distances for which, from what I understand so far, he may or may not have to make calibrations. How is he supposed to quickly and efficiently go about taking accurate shots?

Snipers typically have time to sight their scopes in and take as much into consideration as possible.

 

For the rest, I'm not interested in telling you how to be an efficient sniper.

[swansont]

That sounds like doing more than necessary. If the gun is sighted such that while aiming it points slightly upwards, then why do you need to aim a little below target? Why not just directly at it if the gun is already sighted to compensate the gravitational pull?

 

 

The compensation only works for one distance (which could be zero). So that technique works under a specific set of conditions.

 

e.g. if your muzzle velocity is 500 m/s and your target is 50 m away, travel time is roughly 1/10 second and the bullet will drop ~5 cm. So you can adjust your sights to compensate for that 5 cm. But if the target is 100 m away, the bullet will drop ~20 cm. It's not linear in time. So a sighting adjustment for a 5 cm drop at 50 m will be 10 cm when you double the distance, and you'll be low if you don't make further compensation. (And you can reverse that situation, if you've sighted in for a 100 m target and now you're shooting at one 50m away)

 

And these numbers all change if you change ammo loads and the muzzle velocity is different.