THAT explains it...

[Albtraum]

So I'm taking a physics class, and throughout the semester, we've gone over a variety of topics that can be related to shooting, like: dropping an object, and throwing that object parallel to the ground, which lands first? (Dropping a bullet, and simultaneously firing a bullet straight ahead 90 degrees to the ground) Both will land at the exact same time, gravity exerts the same force on both objects equally, and brings them down simultaneously.

Now for a concept the professor covered last night, dealing with energy and heat... if you heat up a metal ring, imagine a steel washer, does the hole diameter increase, decrease, or stay the same? You should know that metal expands with heat, and the molecules expand in all directions.







Well, the hole will actually grow bigger, since more mass is on the outside, so the inside and outside diameters both increase...

After this, I thought of a rifle barrel heating up as more and more rounds go through it... the bore expands ever-so-slightly, that the bullets are not gripping the rifling in the same way as when the bore/barrel is cool, and that is how accuracy diminishes with rapid fire/ shooting with a hot barrel...

Kinda of a simple concept, but if you look at the details it, you really get a grasp of how and why it happens.
Just thought I'd share.

[firefighter1635]

Neat hearing it the physics way, thanks.

[millwright]

Originally Posted by Albtraum

So I'm taking a physics class, and throughout the semester, we've gone over a variety of topics that can be related to shooting, like: dropping an object, and throwing that object parallel to the ground, which lands first? (Dropping a bullet, and simultaneously firing a bullet straight ahead 90 degrees to the ground) Both will land at the exact same time, gravity exerts the same force on both objects equally, and brings them down simultaneously.

Now for a concept the professor covered last night, dealing with energy and heat... if you heat up a metal ring, imagine a steel washer, does the hole diameter increase, decrease, or stay the same? You should know that metal expands with heat, and the molecules expand in all directions.







Well, the hole will actually grow bigger, since more mass is on the outside, so the inside and outside diameters both increase...

After this, I thought of a rifle barrel heating up as more and more rounds go through it... the bore expands ever-so-slightly, that the bullets are not gripping the rifling in the same way as when the bore/barrel is cool, and that is how accuracy diminishes with rapid fire/ shooting with a hot barrel...

Kinda of a simple concept, but if you look at the details it, you really get a grasp of how and why it happens.
Just thought I'd share.

Waal, your example has a "yes and no" answer. Been a mechanic for more than fifty years and can cite countless examples counter-supportive. Your washer/rifle barrel example isn't very good due to mass/expansion ratio issues. Heating a large mass via the bore axis results in initial bore shrinkage due to the resistance of the surrounding cold metal. In the case cited, the bore will return to (calculable) "size" when the barrel becomes isothermal; that is of uniform temperature.. Anyone trying to remove/install pump impellers has learned this first hand. Manipulating/controlling dimensional changes is a mechanic's stock in trade. The same principles apply to your application. >MW

[armedandsafe]

I've had two different rifles which shot progressively tighter groups as the barrel heated. As it was 1000 yard competition, the barrels never got THAT hot. Also, we were shooting in high ambient temperatures, usually in the 90 - 115F range.

Which doesn't disprove or prove either of the two above posts.

Pops

[WHSmithIV]

Originally Posted by Albtraum

So I'm taking a physics class, and throughout the semester, we've gone over a variety of topics that can be related to shooting, like: dropping an object, and throwing that object parallel to the ground, which lands first? (Dropping a bullet, and simultaneously firing a bullet straight ahead 90 degrees to the ground) Both will land at the exact same time, gravity exerts the same force on both objects equally, and brings them down simultaneously.

This is actually only true in a vacuum and provided the dropped bullet starts it's fall at the exact same instant that the shot bullet leaves the barrel. The bullet travelling through the air builds a measurable amount of lift due to it's shape and therefore actually has a flight characteristic. The falling bullet does not benefit from the lift during travel so therefore will hit the ground first.

[deadin]

I don't see how a spinning symmetrical object could generate any "lift". All of the aerodynamic forces would act equally on all surfaces and therefore no lift would be present. The only forces that come into play are velocity, drag and gravity. Velocity and drag vectors are in horizontal opposition and would eventually cancel each other out.
That leaves gravity which has a perpendicular vector. The only catch is that in the real world the surface of the earth is curved so a bullet fired horizontally actually will have slightly farther to fall then the one dropped at the muzzle.

[WHSmithIV]

Bullets do indeed get a lift factor - the tail end of the bullet has more weight than the nose so the back side of the bullet goes through the air a minute fraction lower than the nose. The bullet isn't going through the air parallel to the surface below and picks up a small amount of lift due to the angle of its flight very much like a flat wing would get at an angle.

[WHSmithIV]

I just did a check on my own common sense - Mythbusters actually proved this, then another science site made independent calculations and proved it again. The dropped bullet will hit the ground first every time. One of the factors they point out is air resistance. The dropped bullet only suffers air resistance in the Y direction that is not happening to the fired bullet until its lost momentum in the X direction from air resistance.

So, what the professor was teaching is indeed true only in a vacuum.

[WHSmithIV]

Kinda of a simple concept, but if you look at the details it, you really get a grasp of how and why it happens.
Just thought I'd share.

Albtraum - thanks for sharing this - you got me to do some research into some areas where I learned a few things I had never thought of. Here's a link to some really good descriptions of the forces involved. I really enjoyed the long range factors section

http://en.wikipedia.org/wiki/Externa..._range_factors

[Blackhawk Dave]

As an aside about the heat factor, when I was at Boy Scout camp, a counsellor demonstrated the effect of heat from both the firing of a rifle and friction by shooting a gallon jar of gas. Resultant explosion was quite impressive to a bunch of Scouts.

[deadin]

But the back end of the bullet will have more surface area then the front end and therefore should drop slower because of air resistance allowing the front end to catch up with it.
Besides gravity isn't picky, it affects everything the same regardless of weight. (Remember the old pound of feathers vs. pound of lead theory? Gravity will work the same on each. Only surface area will change the equation.)

[GunnyGene]

To add to the question: If you fire a standard rifle bullet - say 7.62 - straight up, when it falls will it fall nose first, tail first, or side first? And how fast will fall (approximate terminal velocity)?

[WHSmithIV]

The main factor influencing everything is of course that the projectile is travelling at speed through air whereas the dropped bullet has very little air influence by comparison.

[Buckshot]

I enjoy Mythbusters a great deal, but their science is frequently faulty. (Or more often incomplete.) Take them as gospel at your own risk.

The bit about the vacuum is to remove the differences in aerodynamic properties. Dropping a feather vs. a cannon ball for instance. Take two identical objects of the same mass - two identical bullets - and they WILL hit the ground at the same time. One being fired and one being dropped makes no difference.

The key to the whole thing is firing the bullet in such a way as to be the same height above the surface as the dropped bullet, and to never RISE ABOVE that relative distance. Extremely difficult to do, or judge the success of without effecting the path.

The idea that anything about the shape of a standard bullet producing lift in a vertical plane away from the ground is specious at best. I've NEVER seen or heard of any evidence in ballistics of that effect, nor does anything suggest it.

As for GunnyGene's question, Adam and Jaime did explore this very subject. Keeping in mind the aforementioned caveat about MB, they determined that once the bullet loses the stabilizing effect of the spin imparted by the rifling - likely near apogee - the bullet tumbles, and while it can land with enough force to give you a nasty thump it likely does not have enough oomph to deliver a fatal wound. I wouldn't want to be the one to test that however. There are stories...

[NRA_guy]

Originally Posted by WHSmithIV

The main factor influencing everything is of course that the projectile is travelling at speed through air whereas the dropped bullet has very little air influence by comparison.

Yeah, but you have to think in terms of vectors: friction force (from the air) only works in the direction opposite to the velocity. So the 2 bullets see the same friction force in the vertical direction.

The horizontal friction force acting on the fired bullet has no influence upon the vertical acceleration (rate of fall).

Obviously they also see the same gravitational force, too.

F=ma is the same in the vertical direction: F is the same, m is the same, and a (gravity) is the same.

So, if the fired bullet takes longer to hit the surface, it has got to be lift causing the difference.

That, of course, assumes the Earth is flat.

[goofy]

WOW! This is over my head.
So what is being said is that if I hold a bullet 4' off the ground and let it drop the same time I shoot one that is 4' from the ground(level with the ground) both will hit the ground at the same time?
And the effect of the twist, speed,of the shot round does not change the answer?
Mike

[76Highboy]

Originally Posted by deadin

But the back end of the bullet will have more surface area then the front end and therefore should drop slower because of air resistance allowing the front end to catch up with it.
Besides gravity isn't picky, it affects everything the same regardless of weight. (Remember the old pound of feathers vs. pound of lead theory? Gravity will work the same on each. Only surface area will change the equation.)

I have to go with deadin on this one. I have a degree in Electronics and know the theory. A spinning bullet will not increase in altitude at all. It is subject to the effects of gravity no more ofr no less then a bullet that is dropped from the muzzle.

Myth busters is entertaining but they are not 100% correct on everything.

[tcox4freedom]

All you smart guys make my head hurt!

[Appliancedude]

Originally Posted by tcox4freedom

All you smart guys make my head hurt!

Way over my feeble little mind

[Old Grump]

Originally Posted by GunnyGene

To add to the question: If you fire a standard rifle bullet - say 7.62 - straight up, when it falls will it fall nose first, tail first, or side first? And how fast will fall (approximate terminal velocity)?

Tail first, Read Hatcher, the only way it will come down at any other angle will be if it hits something or air turbulence makes it tumble and that would be a lot of turbulence. The spin of the bullet stabilizes it in the position it was fired in.

http://www.amazon.com/Hatchers-Noteb.../dp/0811707954

[Caneman]

Originally Posted by Albtraum

Well, the hole will actually grow bigger, since more mass is on the outside, so the inside and outside diameters both increase...

After this, I thought of a rifle barrel heating up as more and more rounds go through it... the bore expands ever-so-slightly, that the bullets are not gripping the rifling in the same way as when the bore/barrel is cool, and that is how accuracy diminishes with rapid fire/ shooting with a hot barrel...

Kinda of a simple concept, but if you look at the details it, you really get a grasp of how and why it happens.
Just thought I'd share.

not only that, but the pressure creates a wave that moves back and forth from breach to barrel until is dampens, as the wave moves it also affects the diameter of the barrel...

[Old Grump]

Originally Posted by goofy

WOW! This is over my head.
So what is being said is that if I hold a bullet 4' off the ground and let it drop the same time I shoot one that is 4' from the ground(level with the ground) both will hit the ground at the same time?
And the effect of the twist, speed,of the shot round does not change the answer?
Mike

You got it, all this lift silliness is counteracted by the drag of the bullet, a non factor in a vacuum and one nobody seems to be remembering here.

Bullets have six degrees of dynamic freedom, three translational degrees of freedom and three rotational degrees of freedom. All sporting bullets are spin-stabilized during flight. A flying bullet that is gyroscopically stabilized and trajectories calculated with a three degree of freedom are almost exactly correct. We are only dealing with the three translational degrees of freedom of the bullet, bullet position in downrange, vertical and crossrange coordinates produce a trajectory based on a model that is a point mass with a ballistic coefficient. This is because the spinning bullet is so well stabilized that the rotational motions, other than the spinning motion, are very tiny.

The small rotation downward pitch of the nose of a bullet as it flies along an arced trajectory stays almost exactly parallel to the velocity vector throughout the trajectory. This motion is caused by a very small aerodynamic sideforce on the bullet resulting from a yaw angle known as the “yaw of repose.” The nose of the bullet is pointed very slightly to the right of the trajectory plane for a bullet of right hand spin, or vice versa for a left hand spin.

There is a small crossrange deflection of the bullet, to the right for RH spin caused by the tiny aerodynamic sideforce on the bullet resulting from the yaw of repose.

The bullet turning horizontally to the right or left to follow a crosswind, or turning upward or downward to follow a vertical wind. This turning motion causes a large crossrange deflection of the bullet to follow a crosswind, or a large vertical deflection of the bullet to follow a vertical wind. If you have played with gyroscopes and understand gyroscopic precession you can follow this argument.

A tiny vertical deflection is caused by a the aerodynamic lift force, or negative lift force, on the bullet, which is necessary to make the bullet turn to follow the crosswind.

A tiny horizontal deflection of the bullet together with the large vertical deflection, resulting from a vertical wind is caused by a tiny aerodynamic sideforce on the bullet, which makes the bullet turn upward or downward to follow the vertical wind.

In general they are observable only at longer ranges of 300 yards or more. This is for two reasons. First, as a bullet exits the muzzle with some ballistic yaw, generally an angle near one degree. This yaw causes the bullet to precess, or cone about the velocity vector. As the bullet flies, this coning motion damps out or damps to some minimum value over the first 200 yards. The second reason is that the small effects grow with range flight time. They are overwhelmed by the coning motion at short ranges, but they become observable at longer ranges when the coning motion damps out.

Is your head hurting yet. This what us old shooters are referring to when we say the bullet goes to sleep. We don't put the good match ammo in the gun till we get to 300 yards or beyond. Up till then a plain old spitzer point flat based bullet will do as well or better at short ranges like 200 yards and under. Now back to the discussion, to make the experiment work you need a vacuum or a dead calm, low humidity, low pressure day and it will be close but not quite the same. Math don't lie but as presented they left out a whole semi trailer full of variables.

[aa1911]

someone finally talked about the spin! I was begining to think that was getting ignored.

I usually love arguments like this, but haven't had enough coffee yet to even add my .02 so I'll leave you guys to it.