Really good AGW this month

[Scubashot]

Sounds like I might have to get my pennies out this month to look at Jim's article to see which myths are included. I wold say that 99% of what I have seen on YouTube contains errors, some serious, some not so serious. The internet forums as well are places where myths prosper and gain credulity.
I also have to say that some of the myths are often to be found in the magazines as well. Among the ones I have seen are, that longer pellets take more side wind as there is more side area for the wind to blow on, pellets are drag stabilised, pellet A is more accurate than pellet B because it is more stable and, quite recently, that if you fire a pellet horrizontally and simultaneously drop one they will both hit the ground at the same time.
Unfortunately myths are everywhere and are very difficult to displace once they have become established.

Hot off an educational/science site on the web:
http://www.school-for-champions.com/...m#.WMUfwrynxDu


Shooting and dropping a bullet

If you would shoot a bullet from a gun exactly parallel to the Earth's surface, the motion of the bullet would have no effect on how gravity acts on the bullet. In other words, the bullet would drop at the same rate as a stationary object.

Dropped bullet and shot bullet hit the ground at the same time


Many people don't believe that if you held a rifle or handgun parallel to the ground and at the same time you shot the bullet, you dropped another bullet from the same height, both bullets would both hit the ground at the same time. However, it is a fact.

Exception

An exception to this phenomenon would be if the bullet or object was able to travel so many miles or kilometers that the curvature of the Earth came into play. In such a situation, the bullet would take slightly longer to hit the ground, because the displacement to the ground was greater due to the Earth's curvature.

Example

If you shot a bullet at 900 m/s from a rifle that was 1.5 m above the ground, how far would the bullet fly until it hit the ground? Discount air resistance and assume the rifle is parallel to the ground.

Solution

x = vs√(2y/g)

x = (900 m/s)√[2*(1.5 m)/(9.8 m/s2)]

x = (900 m/s)√(0.306 s2)

x = (900 m/s)(0.553 s)

x = 498 m or 1634 ft

Summary

An object moving sideways or parallel to the Earth's surface will fall at the same rate as one that is simply dropped. The equation for the displacement of the object before it hits the ground can be derived from the gravity equations for falling objects. An exception is if the object moves so fast or far that the curvature of the Earth comes into play during its fall to the ground.

[where's it gone]

?..... make it difficult to read.
Please stop doing it!
#justsaying

As an older reader of Airgun World, I know my eyesight is not what it was. I find the font of the magazine a tiny bit on the small size making reading it not so enjoyable as it was. Older editions a few years back, the font was bigger and a shade darker. While having a clear out, I found some copies of Airgunner, a magazine perceived to be for the younger reader. The font was larger and more bold, making it an easier read.
I've been an Airgun World subscriber for some time, but I was thinking of changing subscription.
I thought this month's issue (April) of A/G World was nothing special, about average. As a school report would say ' ....satisfactory but room for improvement ).

[Terry D]

I thought this month's issue (April) of A/G World was nothing special, about average. As a school report would say ' ....satisfactory but room for improvement ).

As ever, all constructive suggestions are always welcome, WIG.

[ballisticboy]

Hot off an educational/science site on the web:
http://www.school-for-champions.com/...m#.WMUfwrynxDu


Shooting and dropping a bullet

If you would shoot a bullet from a gun exactly parallel to the Earth's surface, the motion of the bullet would have no effect on how gravity acts on the bullet. In other words, the bullet would drop at the same rate as a stationary object.

Dropped bullet and shot bullet hit the ground at the same time


Many people don't believe that if you held a rifle or handgun parallel to the ground and at the same time you shot the bullet, you dropped another bullet from the same height, both bullets would both hit the ground at the same time. However, it is a fact.

Exception

An exception to this phenomenon would be if the bullet or object was able to travel so many miles or kilometers that the curvature of the Earth came into play. In such a situation, the bullet would take slightly longer to hit the ground, because the displacement to the ground was greater due to the Earth's curvature.

Example

If you shot a bullet at 900 m/s from a rifle that was 1.5 m above the ground, how far would the bullet fly until it hit the ground? Discount air resistance and assume the rifle is parallel to the ground.

Solution

x = vs√(2y/g)

x = (900 m/s)√[2*(1.5 m)/(9.8 m/s2)]

x = (900 m/s)√(0.306 s2)

x = (900 m/s)(0.553 s)

x = 498 m or 1634 ft

Summary

An object moving sideways or parallel to the Earth's surface will fall at the same rate as one that is simply dropped. The equation for the displacement of the object before it hits the ground can be derived from the gravity equations for falling objects. An exception is if the object moves so fast or far that the curvature of the Earth comes into play during its fall to the ground.

Unfortunately you have ignored the aerodynamic drag and lift of the projectile in your calculations which are much simplified for education purposes.
As the trajectory of the projectile curves down towards the ground due to gravity there is a component of the drag force acting in the vertical plane. This has the effect of opposing the gravitational force and thus reducing the effective gravitational acceleration. The dropped projectile will also have an air drag component working on it but that will normally be travelling much slower and thus is much less. Your calculation would be correct on the moon where there is no air drag but unfortunately is not correct on the earths surface.
In real life for a spinning projectile there is also a vertical yaw of repose which will produce a vertical lft force to oppose the gravitational pull on the projectile but this is normally much less than the drag effect on bullets at low angles which have a small vertical yaw of repose.
Using Chairgun you can see the drag effect on pellets by setting the sight height to zero and the zero range as close to 0 as possible (2 yards was the smallest I managed). Using the time of flight and the acceleration due to gravity you will get a drop distance significantly greater than the trajectory calculated drop (which will have a slight error due to the sight zero distance being more than 0 yards (up to .5 inches at 50 yards) but not enough to cancel the effect and much less than the calculated and modelled differences which are around 1.4 inches at 50 yards for a .22 pellet)
Just goes to show you cannot believe everything you read on the internet.

[Scubashot]

Forgive my ignorance, but how does a symmetrical rotating pellet generate a vertical lift force that isn't balanced by equal forces around the circumference of the pellet?
Is it related to the pellet adopting a nose down attitude as gravity acts upon it and it starts to descend? Does this somehow create a low pressure zone above and behind the pellet - a la Benoulli, allowing a zone of higher pressure in front of and below the pellet, to retard its descent?
Sounds good even if it's complete nonsense!

[Scubashot]

And I suppose in fairness to the educational website example, they do say "discount air resistance" which I guess should include effects of turbulence.

[Missed_dinner]

Mythbusters proved the bullet drop theory with a practical demonstration.

[clarky]

....just read it today ....not bad at all.

[ballisticboy]

Forgive my ignorance, but how does a symmetrical rotating pellet generate a vertical lift force that isn't balanced by equal forces around the circumference of the pellet?
Is it related to the pellet adopting a nose down attitude as gravity acts upon it and it starts to descend? Does this somehow create a low pressure zone above and behind the pellet - a la Benoulli, allowing a zone of higher pressure in front of and below the pellet, to retard its descent?
Sounds good even if it's complete nonsense!

As the pellet begins to fall towards the ground the trajectory begins to curve away from the direction in which the pellet is pointing. A stable pellet will turn to follow the trajectory and the gyroscopic response to turning onto the trajectory is to produce a small side yaw called the yaw of repose which is what gives spin drift. The gyroscopic response to the side yaw angle is to produce a small yaw angle in the vertical plane which is called the vertical yaw of repose and this is what produces a small vertical force. On large spinning shell it is quite a large significant force, particularly in high angle fire. For pellets and bullets the angles are much smaller and therefore the force is very small. As I said before it is the drag force which produces most of the effect.

Mythbusters proved the bullet drop theory with a practical demonstration.

Mythbusters couldn't prove anything scientific if their lives depended on it. Their "experiments" are poorly conceived, hopelessly uncontrolled and lacking in the basic knowledge of what they are trying to demonstrate. But lets suppose you are right, that would mean that every fire control computer for every gun for just about every army in the world is wrong along with every ballistic test carried out under carefully controlled conditions to produce the data necessary for accurate long range fire. Do you really think that is very likely?

[Mole trapper]

As always a good read, only thing in my opinion detracts from the enjoyment is this relatively new phenomenon where in the hunting articles, the authors insist on stating "I was glad I'd made my first kill" , "it's great to get a kill", it would be so less provocative if it were termed I had got another for the pot etc. I know that it's pandering to the lentil munching libtards, but it makes a very different statement when they quote it in their propaganda.
Release the bile now, I know this will get a few backs up.

[where's it gone]

?.. the authors insist on stating "I was glad I'd made my first kill" , "it's great to get a kill", it would be so less provocative if it were termed I had got another for the pot etc....

Not many of us eat rat, crow or magpie. After all, it's a reading magazine, edited by Terry Doe, not 'Kill it,cook it, eat it', presented by Julia Bradbury

[Mole trapper]

Thank you for the gift of laughter!

[Scubashot]

As the pellet begins to fall towards the ground the trajectory begins to curve away from the direction in which the pellet is pointing. A stable pellet will turn to follow the trajectory and the gyroscopic response to turning onto the trajectory is to produce a small side yaw called the yaw of repose which is what gives spin drift. The gyroscopic response to the side yaw angle is to produce a small yaw angle in the vertical plane which is called the vertical yaw of repose and this is what produces a small vertical force. On large spinning shell it is quite a large significant force, particularly in high angle fire. For pellets and bullets the angles are much smaller and therefore the force is very small. As I said before it is the drag force which produces most of the effect.

There's an awful lot going on in the background with spin drift: left or right hand twist rifling changing the direction of spin, coarse or fine "thread" rifling changing the rate of spin, cross winds combining with the Magnus effect to create upward or downward forces, depending upon the directions of spin and crosswind.
Is it actually conceivable that the right conditions could create sufficient downward forces to actually allow the fired pellet to hit the ground before the dropped one?
Enough of this silliness, I'm getting a headache!

[Terry D]

... the authors insist on stating "I was glad I'd made my first kill" , "it's great to get a kill" ...

Hello, MT, and thanks for the constructive criticism, we genuinely do value it.

I have to confess I can't recall those lines being quoted exactly as you've stated them, and 'it's great to get a kill' isn't normally the style of our hunting writers. We're more of a 'it's great to get the first one in the bag' sort of magazine, although it's entirely possible your quote is correct.

The main point is, Airgun World is fully aware of its responsibilities regarding the portrayal of our sport and we take those responsibilities seriously. However, there must be balance and it's also essential that we don't present as being ashamed of what we do. The fact that we enjoy using guns, let alone hunting with them, will always mark us as unacceptable in the eyes of some, and the only way to please such people would be to stop doing what we do.

I think we generally get the balance right, but we'll keep working at our representation and content, guided by the readership. Thanks again for your input, MT, and all the best.

[Seamaster]

As far as Scubashot's observations go, you have to remember, like most theories given in Physics, that you need to preface the statement with the words "in a vacuum".
It's often forgotten but almost always is a given in Physics to eliminate outside influences.

Chris