Pellet Ballistics

[Guest]

Rookie question: does a pellet rise before falling? Just seen a diagram in a book that suggests that they do but my understanding was that this was an illusion because scopes are set to point down slightly and that the pellet comes out straight and just falls away gradually. What's the truth?

[FalconFN]

Gravity acts on a pellet as soon as it leaves the barrel so a pellet shot horizontally would drop short of the target. To get it to a target, say 30 yards away, the barrel will have to be elevated slightly so that the trajectory is that of an arc. The best way to see what happens is to download a free program by Hawke scopes called Chairgun which shows the trajectory of a pellet.

[kent]

No but it might appear to in POINT OF IMPACT in relation to LINE OF SIGHT. With the average airgun the line of sight intersects at two places lets say 8 yds and 28yds. But the pellet aint rising its dropping all the time indeed if you think you have zeroed for the bullet to stike high but usable at the mid point between 8 and 28 then continue to fall into a 28yds zero your about there. After that 28yds zero it continues its downwards flight falling with a progressively and more prononced POI from LOS

[HW682]

this has been discussed a few times and often gets a bit catty.

 

The answer is that it depends on how you define up and down.

If we keep it simple then DOWN is the direction that an object falls if you let go of it. Then lets call UP the opposite direction.

 

In this case, exactly as FalconFN says, a pellet has to rise unless you only want to hit a target below the muzzle of the gun.

 

Some people "APPEAR" to talk nonsense about this subject, but it usually beacuse they are working to a different definition as to what UP means.

 

 

Edited to add a bit more:

If we consider a shooter taking a standing shot at a target. The gun is 5ft above ground and the target is 35 yards away and also 5ft above ground.

 

Q1) Does the pellet RISE between leaving the muzzle and hitting the target? The answer is an obvious yes.

 

Q2) Does the pellet trajectory form a parabola with respect to an imaginary line drawn through the axis of the rifle bore; such that it first deviates away from the bore-line, then curves and comes back towards it, before crossing the bore-line again before hitting the target? The answer is no.

 

The problem is that when people ask "does the pellet RISE?", some will turn it into question 2) and answer "no". Although the person giving the answer probably has a clear mental picture of what they are saying - the OP might take it as a "no" to question 1).

Edited February 15, 2012 by HW682

[richard1951]

HW put that realy well the pellet does not rise but it goes up coz you point the gun up for it to be able to be back to 5 foot when it reaches the terget

[Dekers]

 

Pellets are generally pointed up via the angle of the barrel, just the same they do not rise, they fall from the barrel angle the moment they leave it!

 

Just like wot he said above.

[pimpkiller]

they dont float up or have "lift" they go "up" because the gun is pointing up, its all downhill from there

[sodit]

Rookie question: does a pellet rise before falling? Just seen a diagram in a book that suggests that they do but my understanding was that this was an illusion because scopes are set to point down slightly and that the pellet comes out straight and just falls away gradually. What's the truth?

 

 

Have a look at

 

1 http://www.chuckhawks.com/bullet_trajectory.htm This is for bullets but same thing for pellets but slower.

 

2 http://viriato.net/airgunning/bfta_setup_manual.pdf Look at chapter 6.1 for explanation.

 

Just be happy you didnt have to cover this in mechanics theory for some reason it did my head in probably co I'm thick :o

 

 

Neil

Edited February 16, 2012 by sodit

[HW682]

Quote from the chuckhawkes link:

Fact or Myth. So, does a bullet rise after it leaves the muzzle? One says, "yes." Another says, "no." Who is correct? Both could be correct because of different meanings associated with the word, "rise." They might argue incessantly, but their argument will not change the physical aspects of the path of the bullet. If they would concentrate on discussing the physical events, they would eventually conclude that they were each using the word, "rise," differently or that one of them did not understand elementary ballistics.

 

 

which is exactly what I said. I am sure if we had a good diagram of the trajectory of the pellet (almost) all would agree with it. But people disagree on how to describe it.

 

Edit:

I have had a go at a sketch.

It is not to scale and deliberately exaggerated to make it easier to describe what is happening. It represents my earlier example of a standing shot, so scope and target are both 5ft above the ground and the target is say 35 yards away, where the scope is zeroed.

Dotted line "A" is the scope axis which points stahight at the target.

Dashed line "B" is along the axis of the bore of the barrel.

Solid line "C" is the path of the pellet (assume it carries on after passing through paper target).

 

The pellet starts off along the bore-line, but immediately drops below it due to gravity.

The maximum height of the pellet at distance "d2" is greater than the starting height of the pellet at distance "d1". Therefore, using simple English, the pellet rises (above ground) at mid distance, but never crosses "above" the bore-line.

 

Anyone agree or disagree?

HW682

(I know it is over-simplified, and eg the point of aim won't be through the true centre axis of the scope because the reticle will be off-centre etc etc but it is just intended to show the approx. path a typical pellet will take.)

Edited February 16, 2012 by HW682

[bedwards1966]

HW682 - well put, it describes it perfectly

[Guest]

So, I think link 2 from Sodit is what I had understood

 

http://viriato.net/airgunning/bfta_setup_manual.pdf

 

HW682's diagram would agree if the barrel was parallel to the ground instead of showing an upward slope. I guess it's two ways to look at the same thing.

Edited February 16, 2012 by Guest

[HW682]

DC177

a quick look through the link seems to show that all the pellets are landing below the staring point, which would be like taking a standing shot and aiming at something on the floor. The only way to hit a target at the same height as the muzzle is to shoot slightly up first. Also as the distance to the target gets longer you need to point upwards even to hit a lower target.

 

Edit: just had a better look. The author seems to be deliberately twisting things to prove his assertion that "the pellet doesn't rise". At the bottom of page 20 it says:

If we want to accurately

shoot at a target we need to elevate the muzzle in order to raise the Point-of- impact (POI).

This is what happens when we mount a scope. You are looking straight at the target but

the scope is set in such a way that the rifle is actually pointing upwards.

 

But then fig 2 shows the barrel horizontal, and the scope is aiming below the muzzle. It seems to have done this just to make the statement that

The pellet is not

initially rising, as is often believed.

 

Well, I don't think people believe that the pellet is rising if the barrel starts off horizontal. But this is no use unless you always shoot below the height of the muzzle. If you want to shoot higher, you have to point the barrel up, just as in my sketch, just as the article quotes on page 20 and just as it shows in the next fig3 - but even then it still shows the pellet hitting below the height of the muzzle The only way to hit higher is to raise the angle of the muzzle even further.

 

In summary: if you want to shoot downwards, then the pellet doesn't rise. If you want to hit a higher target then the pellet has to go up or rise or call it want you want. Just follow the diagram and don't worry what it is called

Edited February 17, 2012 by HW682

[sodit]

Hey folks dont make it hard (oooeer matron )

 

In the physics (and real world) world gun horizontal to ground pellet falls due to gravity as soon as it leaves the barrel it cannot do anything else there is no (significant or useful) acceleration after leaving the barrel to enable it to overcome gravity. (Is gravity real or does the world just suck!)

 

In the real shooting world by sighting the weapon we allow for this by changing the angle of the barrel to enable us to hit our target as required. :o

 

HW682 had it right in his first description I just added the links cos I usually find a picture helps you understand the written word because as stated I am thick :o.

 

If you look at the replies most people have it right one way or the other.

 

To answer the original question as asked. No, but due to sighting the weapon the ballistic curve gives that impression.

 

When you read the gentleman who answers these kind of questions in Shooting gun regarding bullet flight he generally mentions the angle of the weapon. (another oooeer matron moment )

 

Just thought I would stir the pot a little more

 

To all those offended by my thoughts READ THE FIRST LINE OF MY SIGNATURE and if I have it totally wrong then politely let me know

 

Sodit :yp:

[FalconFN]

I don't think we should get too bogged down with semantics, the basic fact is that a pellets trajectory is such that it will have to move away from the Earth (rise, if you like) before it starts to drop if it is to reach a target that is horizontal to the rifle. Nobody in their right mind would think that anyone is suggesting that it would leave the barrel, change direction, do a backflip, and then dive towards the target. HW682 explains it well, which is something I've failed to do in the past.

[Guest]

Ok, I see what HW692 means now, and the set up manual in the link does contradict itself. I be a slow learner... :blink:

[richard1951]

This is a very hard thing to explain , there are at least 6 of us that know exactly what happens and how it works and we all have explained in a slightly different way to you the same thing. but i think you now have got it , you will now know what happens but weather you can pass this on is another thing . lol