Bullet "Rise" - Dispell the Myth
 

We had the guy at the gun store trying to tell us that the bullet does not come out of the barrel in a straight line. He was telling us the old myth about how the bullet actually rises up at first. When we suggested that this was not possible, he told us that the bullet planes like a kite on the air currents. I didn’t want to argue with him because I had already argued with him about the point of impact at different ranges varying with the distance the scope is from the barrel.

RE: Bullet "Rise" - Dispell the Myth
 

Holy Cow, I wouldn't know how to respond to that ignorance. I might have to just sigh, and walk away.

RE: Bullet "Rise" - Dispell the Myth
 

A lot (maybe most) of the guys working at gun or hunting related stores don't have a clue about what they're selling. Not long ago I was at a local outdoor store and overheard the guy behind the counter explaining to a customer why brand X scope was better than brand Y scope. "This scope here's the one to go with, it's got real strong parallax", he says. I started to ask him to explain parallax to me (which I already understand) for the amusement I would have gotten out of his explanation, but I just grinned and walked away. I think the customer was on to him too, he walked out without buying either scope.

RE: Bullet "Rise" - Dispell the Myth
 

Barnes, That's one of those situations where you just want to walk to the nearest brick wall and start banging your head on it. Because you know you'll have better luck with the wall and who knows if do it long enough you might get lucky and forget you even heard that dis-logic come out of another human beings mount!:D:D

SolidarityMan, It never ceases to amaze me that some sales people just can't seem to say,"I don't know" or I'm not sure." When I find one that does it's a relief because then I can take the rest of what they said more seriously. :eek:

RE: Bullet "Rise" - Dispell the Myth
 

Well, if we want to play symantics, one could say that a bullet "rising' from the muzzle after being fired is, in most cases, technically correct if you're referring to the path of the bullet relative to the line-of-sight. Generally a bullet "rises" or ascends relative to the LOS and the ground before it decends toward the ground. But whether the bullet is actually moving upward or downward, it is always falling due to the unresisted force of gravity.

The bullet, however, does not create any lifting force that causes it to fly in the gravity defying sense.

Mike

RE: Bullet "Rise" - Dispell the Myth
 

Hmm, you got a point drift. So techncially the guy behind the counter is right except for the whole kite stupidy. I think we all owe him a appology. Cause this is what he had to mean, cause a bullet rising with no pressure deltas like a airplane wing is impossible. :D

RE: Bullet "Rise" - Dispell the Myth
 

I know what you're saying is true, but to make it even more clear, shouldn't we say that it rises in relation to LOS because the barrel is pointed upward in relation to LOS. IT rises up from the end of the barrel because the barrel is actually pointed upward. We do this so that the trajectory of the bullet from the barrel (pointed ever so slightly upward) intersects LOS at a certain point (our zero point). The confusion is that the bullet may continue to go upwards beyond the LOS before it falls back down to LOS and below. This is what the poor ignorant clerk didn't understand and was groping for an explanation for. Probalby someone else who didn't know had told him. I know I was confused until I saw it in a diagram. FWIW

RE: Bullet "Rise" - Dispell the Myth
 

Well, if we really want to break it down (symantically or otherwise LOL):

As soon as the bullet leaves the barrel it starts "falling" in relation to the plane of the barrel. The rise is in relation to LOS which has no physical bearing on the bullet's path what so ever. Just being a little anal here...LOL! But it seems this thread was going that way any how. :D

RE: Bullet "Rise" - Dispell the Myth
 

If the barrel is aimed flat the bullet will not rise at all, it will immediately start to drop. the key is that the barrel isnt laid out flat, the SCOPE is. So to get the point of impact on the ceter of the crosshairs at a give distance, we LAUNCH the bullet upwards, it doesnt get any aerodynamic lift, only whatever trajectory is inherent in the angle at which we launch it upward..

RE: Bullet "Rise" - Dispell the Myth
 

I think you read my post too fast. You missed the part about the bullet path in relation to the plane of the barrel. Yes, the bullet "rises" in relation to the Line Of Sight, but not the the plane of the barrel which will be angled "up" in relation to the line of sight (not necessarily the horizan, but that's another can of worms). The LOS is once again confusing the issue me thinks. The original post was really about how the rise in the path of the bullet in relation to the LOS was being confused with an old myth that somehow the bullet takes off and actually rises in relation to the plane the barrel was on when fired. What I was saying was that the bullet is dropping down from the plane of the barrel and never rises above it.

RE: Bullet "Rise" - Dispell the Myth
 

People in gunshops are human too. If they don't know any better they will not only subscribe to but will also spread such myths as brush busting bullets, rising bullets, and bullets/calibers that have so much energy that they will litteraly knock 200 lb animals, 2 legged or 4 legged, over after the animal is completely flung in the air.

RE: Bullet "Rise" - Dispell the Myth
 

I was with Barnes yesterday when we went to the gun shop. I had Barnes post this because he is a re-loader and he knows a little bit more about ballistics than I do.

I wanted to get a scope mounted with lower rings because the old set-up had see-through mounts and when sighting it in at 50 and 100 yards, the difference of point of impact was pretty different. We posted the problem on the board and we got a lot of explanations on why this was happening. Yesterday when I explained to him the problem with the mounts, he said that it shouldn’t be an issue (that’s another can of worms). We got into a discussion about sighting in scopes and he made a comment that in warmer weather, the heat rising from the ground will cause the bullet to rise (maybe I should of asked him if a bullet sinks faster because of the cold air, just to get a laugh). I don’t know much about ballistics, but I told him that a bullet only rises due to the barrel being pointed up and that it never breaks the plane of the barrel, he disagreed and gave me this air pressure theory and something to due about a vacuum the bullet causes when being fired from the gun. Almost appeared that the bullets he fires have wings and a flight control stick.

Sad thing is, this guy mounted my scope, however, I think he knew what he was doing with the mounting part. He’s one of those guys that work at a mechanics shop and only changes and balances tires; occasionally he may change the oil.

RE: Bullet "Rise" - Dispell the Myth
 

With idiots like this that have no clue on ballistics, I can almost see how other idiots came to believe "guns kill people"-- Air-Bullet-Control simply had the wrong coordinates and misdirected the flight paths!!! [:o]

RE: Bullet "Rise" - Dispell the Myth
 

This is really technical, and pretty picky, and I really don't like applying my job to my pleasure, but I've got to comment.

My granddad used to have a saying "don't speak on what you don't know"....in this case, you are both guilty.

The guy is wrong because of his reasoning...it isn't exactly air currents that raise a bullet. That is a myth, very similar to the "bullet shedding myth", supposedly bullets sand themselves on the air as they fly because they are so fast, which is bogus. But I digress.

You are wrong because this actually CAN happen. It's called the magnus effect. Although I've never studied projectiles like bullets for this effect, I have studied the analogous scenario of a spinning rod (perpendicular to fluid flow) in a pipe of flowing fluids. If the pipe where stationary, two basically symmetrical "boundary layers" of static fluid would form on either side of the rod, in a fairly rapid flow, these layers detach in what is known as vortex shedding, which caused the failure of the Tacoma Narrows bridge in case you're curious....It's also why a flag whips back and forth in the wind.

However, if you start spinning the rod, these boundary layers become uneven, producing a velocity difference between the two "sides" of the rod, which creates a pressure difference similar to that of an airplane wing. So, this is VERY minimal in air because it is a low viscosity fluid (yes, it's a fluid, even if it isn't a liquid).

For example, if you're looking at the tail of your bullet in flight, and you have a strong wind left to right, and your bullet is rotating counter-clockwise as viewed from behind, this will induce a more rapid drop in your bullet...the same bullet in a right to left wind would raise.

It's a real thing given the right conditions. It wouldn't happen in still air, and it likely gets attributed to the wind any way if it were to be noticed on a windy day...the bullet drift horizontally with the wind would likely be much greater than the vertical drift caused by the magnus effect.

If I recall correctly, this myth honestly comes from civil war times. Soldiers would aim their cannons directly at the front line of soldiers coming at them, but the ball would "sail" over the first line and take out men in the second or third...which I would be prone to believing was an effect of their design, rather than the magnus effect.

RE: Bullet "Rise" - Dispell the Myth
 

Joe D., Read "Sniper" by Adrian Gilbert, I want to say chapter 7, but I'm not sure....bullet "Rise" in hot weather does honestly occur, but it isn't the bullet that's rising, it's the image of your target. It's called known as a mirage, and pretty accurately so. The hazy lines you notice on the roadway occur over all sorts of land, just to a lesser degree. The heated, rising air bends light, so what you're seeing isn't exactly what you're looking at.

Mirage can also be used to calculate wind speed, adjust your scope slightly out of focus and you can clearly see the mirage "lines" or waves, in a good wind, they'll be leaning one way or the other, I can't recall right now where exactly you're supposed to aim relative to the lines though? It's not even with the bottom, it seems like there is a rule of 1/4 in there somewhere?

Read military sniper manuals or shooting books written by retired snipers and you'll find a wealth of information.

Mirage and magnus effect are minimal, most hunters will never notice them in their lifetime, because the change in relation of POI and POA over typical hunting ranges isn't enough to take your bullet completely off your deer. Most guys will attribute a miss at that range to their "accuracy" or the wind, not to the smaller ambient environmental effects.

RE: Bullet "Rise" - Dispell the Myth
 

Nomercy,

Then the real question is this...does the magnus effect due to a strong crosswind coming from the correct direction create enough lifting force to balance or overcome the force of gravity, under REALISTIC shooting conditions?

If it does, then a bullet could in fact experience enough body lift to actually climb above the plane of the barrel. If not, one could say that the force simply acts to retard the decent of the projective by cancelling out some of the accelleration created by gravity (like a parachute).

Mike

RE: Bullet "Rise" - Dispell the Myth
 

Here's a little scenario I love to watch people try and wrap their brains around. If they get it, and it usually takes a little extra expanation, then they are in the right frame of mind to get other aspects of ballistics.

You have two bullets, one that you are going to drop by hand and one that will be fired from a gun. The gun's barrel is perfectly level with a perfectly level floor that extends for miles. If you drop your bullet from the same height of the gun barrel at the exact moment the fired bullet leaves the barrel then both bullets will hit the floor at the same time. (See attatched picture)

It's really cool seeing the "lights come on" when someone gets it.

RE: Bullet "Rise" - Dispell the Myth
 

Another thing, that i've SEEN happen is, ammo fired in HOT weather, the powder makes more pressure (pressure = fps) and so shoots slightly flatter. Shoot the same ammo in very cold weather and the V is slower!!

I've seen this many times with 22lr ammo, when winter hunting in cold weather high in the mountains for ptarmigan!!!

Anyway, magnus theory or not, i'm sticking with, bullets start to fall from the time they leave the bbl, and keep on falling!!!

Drilling Man

RE: Bullet "Rise" - Dispell the Myth
 

I agree driftrider. Considering that the viscosity of atmosphere is so minute compared to any liquid. And even in hurricane force winds (which I hope no one will be shooting at a deer then) and the rate of rotation is still only 1 in 10 inches for most rifles (fast time true, but not likely fast enough) and considering the tiny amount of surface area involved compounded by the density of the bullet (it's going to take a lot of lift to noticeably affect something made of lead and copper) that the Magnus effect would probably so small that it would only retard the rate of decent and even then you'd probably need to borrow a lab and a few NASA techs to separate the difference from standard deviation. Here's the real kicker though, using the old .30-06 as an example, the bullet is not just spinning in space it leaves the barrel at 1,984 MPH and if shooting in a 100 MPH crosswind the net effect would be a 0.05% total wind direction change over the surface of the projectile from shooting in calm conditions. That's about 9 degrees from head on and that would definitely not be enough, in my opinion, to generate the Magnus effect in any measurable quantity. Now you're no longer talking about the rotation being perpendicular to the air current, it's nearly parallel to the air current. Keep in mind that's with 100 MPH crosswinds! That's my opinion. But hey, it's been a long time since I was at Purdue and Nomercy, I'd love it if you'd run the numbers and prove me wrong (not with out debate of course ;) ) because I want above all else to learn. In fact if you can demonstrate this does indeed have a quantifiable and meaningful impact on ballistics it will certainly only enrich my knowlege as well as others who read this board and after all that's why most of us are here.

I still believe that the bullet NEVER rises above the plane of the barrel! By the way, every physics model used by "ballistics software" I've tried out agrees with me on that one. If you plot bullet drop you wont find the bullet rising to a positive number at any point. Who knows maybe they "don't of what they speak" either (to paraphrase your post), in which case you could set us all straight.

RE: Bullet "Rise" - Dispell the Myth
 

I agree that any given bullet fired on any given day won't likely see much of a magnus effect...and even if it does, it is very unlikely that it actually rises at any point, as opposed to simply resisting its decent. However, I can say that it is feasible, with the working knowledge I have, that it could occasionally happen in the right conditions that are possible under "natural" and real hunting conditions.

One thing you are mistaken on, the magnus effect has absolutely nothing to do with linear velocity, i.e. the speed of the bullet. It ONLY has to do with the fluid velocity (wind speed) and the rate of rotation or angular velocity...a 3000fps bullet of any diameter coming out of a 1turn/12" bbl is spinning at 180,000rpm, which is pretty quick. See below for details.

This is about to get REALLY long.

Want proof the magnus effect is real? Why do curveballs curve? Check out a golfball when you hit it some time, ever noticed how sometimes they'll climb very sharply if you hit them with a lot of spin?

Ok, if you want numbers, here goes: a 150grn .30-06 bullet at 3000fps from a 1/12" rifle in a 15mph crosswind in air at 40Deg. F:

L=lift exerted on a rotating cylinder PER length

L=pGV, where p=density of fluid (air), V=velocity of fluid (or , G=2*(pi)*radius*v, v=2*(pi)*radius*w, w is angular velocity=linear velocity*rate of twist


SO: L=pGV-->L=p*2*pi*radius*2*pi*radius*linear velocity*rate of twist*wind speed

Throw in a couple conversions, like the radius in inches-->ft, wind speed in mph-->ft/s, and pound(mass) must be converted to pound(force)....this conversion is 1lbf=32.174lbm*ft/second squared.....

Plug in all the numbers and you get 1.07lbf/ft.

I'm going to assign a value now for the average cylindricity of a 150grn .308" bullet. If you assign an average radius of .154" (1/2 of .308"), your spitzer type 3/4" long bullet is likely now only .5" long...so I'll use that length for my effective force length....that's 0.042ft in case you're wondering...

That comes up to 0.045lbf force exerted upwards due to magnus effect (or downward if the wind were switched).

The force of gravity can be calculated Force=mass*acceleration-->150grns*1lbm/7000grns*32.17ft/second squared/32.17lbm*ft/lbf*second squared

That gives a force of gravity of 0.021lbf. Roughly half of that exerted by the magnus forces.

However, this is for a constant 15mph wind, and assumes idealized boundary layer separation (i.e. it doesn't involve boundary layer/vortex shedding), and it doesn't include the boundary layer buffering effect that the linear velocity of the bullet causes (the bullet rushing through the air reduces the magnus moment: the boundary layer is kind of pushed off the back of the bullet). Nor does it account for likely a hundred other effects that algebraic models (which i used for simplicity) can not account for, differential and integral values for the vortex shedding and linear velocity terms.

Do a search on the web for "magnus effect" or magnus moment, and you'll find a wealth of information on the topic.

Here's a website I found interesting, but you'd have to have access to a LOT of constants to use this formula http://www.snipersparadise.com/wound...m#MagnusMoment

Like I said, it's not likely, but experimental and theoretical models have proven the validity of the case.

RE: Bullet "Rise" - Dispell the Myth
 

Well, I can certainly say one thing for certain...

Nomercy must have really paid attention during his math classes!!;)

I actually feel smarter after reading that!:D

Mike

RE: Bullet "Rise" - Dispell the Myth
 

This is good stuff, especially the web site you included. I'm still digesting the info they have. I think the problem arises in the fact that, using your example, a 3000 fps projectile is encountering a 2045 mph head wind. I would think this GREATLY reduces the Magnus Moment. If my thinking is correct, the 2045 mph head wind combined with a 15 mph cross wind would create an effective yaw against the wind of only about 1.3 degrees versus 90 degrees (perpendicular air flow). And as the site says, "The Magnus force vanishes in the absence of rotation and in the absence of a yaw angle." I believe your calcutlations only account for perpendicular air flow. To quote the site further, "The Magnus force is usually very small and mainly depends on bullet geometry, spin rate, velocity and the angle of yaw." This leads me to believe that the head wind (especially in super-sonic flight) nearly negates the Magnus Moment.

The curve ball and the golf ball are spinning on an axis nearly perpendicular to their direction and hence a head wind aproximately equal to their velocity. That's why they encounter a noticable effect. The bullet on the other hand is spinning on an axis parallel to the head wind.

This does raise an interesting question though. In the case of an overstabilized bullet that maintains it's orientation in relation to the plane of the barrel, as the bullet starts to decend toward it's target the effective yaw in relation to the "head wind" would become greater and greater and the Magnus Moment might besome great enough to move the bullet left or right depending on the direction of the rifling.

By the way what number did you use for p? I might have missed it, it's late and I'm tired. :)

RE: Bullet "Rise" - Dispell the Myth
 

This guy is wrong, of course! BUT, there are a LOT of people who believe this!

A lot of people selling gun stuff are totally ignorant about the subject. For example, the other day I was at the local DICK'S "sporting goods" store looking for a couple of scope mount bases.. (Yeah, I know!) Well, I told the genius behind the counter that I wasnted a specific pair of bases. He started lookijng through his assortment of RINGS!!

I said, "those are RINGS. I need bases." I then had to lead him to the portion of the pegboard where the bases were hung up in little plastic bags. "Oh yeah." says he. "Bases." Believe it or not, he did find the right ones. there were two bases in the little bag, but he tried to sell me FOUR because "it says right here on the envelop that you need two." So I said "but there are two in this envelope, and that's how many I need." he says "Well, it's your gun. If you need another envelope of them, I guess you'll just have to come back." I just laughed and said "yes, I guess so! har, har!!"

RE: Bullet "Rise" - Dispell the Myth
 

Well, a bullet DOES actually drop faster in cold air vs warm air. The reason is that cold air is denser, and therefore provides more resistance to the bullet's passage, thus slowing it down faster. (Think of it as lowering the bullet's B.C. a little.) This means that the trajectory curve will be a little steeper when fired in cold air vs warm air. This is one of the reasons artillery firing calculations include both air temperature and local atmospheric pressure in the variables.

RE: Bullet "Rise" - Dispell the Myth
 

After a little sleep and more reading here's what I've come up with:

We've both over looked the fact that the Magnus Moment acts on the Center of Pressure and not the center of gravity. I'm still standing pat on the fact that you don't have a 15 mph perpendicular flowfield but rather a 2000+ mph flowfield that is nearly parallel to the bullet path. As the bullet yaws in respect to the flowfield the Magnus Moment grows in magnitude and changes the yaw because it is acting on the CPM rather than the CG. And to quote another site(http://www.nennstiel-ruprecht.de/bullfly/fig11.htm), "However, the gyroscopic effect also applies for the Magnus moment and the bullet’s axis will be shifted into the direction of the moment. Thus, as far as the conditions of the figure above are valid, the Magnus moment will have a stabilizing effect as it tends to decrease the angle of yaw d." If the CPM is rearward of the CG then the MM will have a destabilizing effect because it will actually increase yaw, eventually causing the bullet to tumble.

Simply put, in the face of the actual flowfield, the Magnus Moment direction is constantly changing in response to yaw and hence is a very important factor in bullet stabilization. So, at no time will Magnus effect lift the entire bullet unless the CPM is behind the CG and the yaw approaches 90 degrees (the point where the MM is at it's greatest magnitude) but at this point the bullet is tumbling out of control and it's time to consider using a new bullet design. Even then the MM is still acting on the CPM and will probably just continue to spin the bullet around the CG in a plane perpendicular to the axis of symmetry.

RE: Bullet "Rise" - Dispell the Myth
 

WOW, you guys are pretty smart about this stuff. I just wanted to clarify something. I think the original post asked if the fired bullet actually rises, and the general opinion is that it does not, which I agree with. However, I have read in several long range shooting manuals that explains the rifling of a barrel does affect the point of imact, but does not impart enough force to make the bullet rise, and for a short period of time, offset gravity. What the books clearly say is that over longe ranges, rifling will impart enough "spin" so that the bullet path is a slight arc (left or right) depending on the orientation of the rifling, so it drops from gravity and also drifts (although very slightly) at the same time. Does this make sense???

Thanks,
CE

RE: Bullet "Rise" - Dispell the Myth
 

Good point, that plus what DM brought up:

This means if you sighted-in in July in 90 deg weather you'd better check your point of impact at the range closer to hunting season when you might be shooting in 10 degree weather!

Now I'm curious, has anyone got any chronograph logs? What I'm wondering is if the chamber temperature (heating up as the gun gets fired over and over) has a noticable effect on velocity and there by affecting the point of impact. This may also be a factor for sighting in for hunting season because your deer is not going to wait there patiently while you fire off a few rounds to warm up the gun to the same temp it was when you put that final adjustment on your scope...LOL!

RE: Bullet "Rise" - Dispell the Myth
 

ColoradoELK, yes it can happen even without a crosswind. The yaw of reprose is most likely the factor when this is obseved.
See:
http://www.snipersparadise.com/wound....htm#yawrepose

Hope this helps.

RE: Bullet "Rise" - Dispell the Myth
 

You are correct that the overall flow field is nearly parallel to the line of flight, however, because it is NOT parallel, I can chose whatever coordinate system I like and apply additive vectors to get the net flow direction (i.e. I take one step forward and one left, I end up moving 1.41steps at 45degrees). So, instead of saying I'm in a 2046mph I can say I'm in a 2045mph head wind with a 15mph cross wind, and have the same effect. In either case, the magnus effect would be virtually the same, because the perpendicular component of the angular flow field is ALWAYS 15mph, whether I say it's 2045.5mph at .46 Seconds of angle or I say it's 2045.45mph head on and 15mph side on.

Accounting for yaw angle isn't necessary if you do this addition. The advantage of it, however, is the ability then to account for the boundary layer buffering and shedding, which I've not yet seen a formula for that doesn't take more calculus to do than I can do in 5min sitting at the computer, and constants for directional drag coefficients or magnus coefficients that would be specific to each individual case.

Also, if I'm reading the figure and text you pointed out correctly (which I think is the same exact figure as one on the site I pointed out above), then the following will happen in my hypothetical 150grn .30-06 bullet...in which the center of pressure WILL be behind the center of gravity, as the relatively large cylindrical body will draw the center of pressure to it, while the center of gravity is shifted slightly forward because of the mass of the tip (assuming that you neglect the density difference in the copper jacket and the lead core, which would shift the Cg rearwards).

This also explains why the magnus force would only temporarily lift a bullet...

The magnus forces would start working, it would lift the bullet, but also turn it to become parallel to the overall flow field (turning your bullet into the wind), this would reduce the magnus lift force considerably...However, it would also be turning your bullet tip INTO the wind, which won't have a net positive effect because of the mass-mass impact of the x-wind and the bullet bluff body...Honeslty, I think there would be no net force in that direction, but more of a torque, so your bullet would become unstable because of the wind and start to gyrate.

So, basically what that figure shows, projectiles will be turned tip wise by a cross wind in addition to their lift, both caused by the magnus effect...this would have a LOT of results, drawing your bullet into the wind (negated by the wind PUSHING back), pointing your bullet into the wind (destabilizing it's flight), and reducing the lift force created by the rotation.

Like I said, no, it's not likely you'll ever see any net positive LIFT due to it, but the force is real, and given the right combination of oddities-which COULD be possible in a hunting environment-it could happen that the magnus force overcome the force of gravity momentarily.

Cut-throat (eldeguello) is correct about the bullets dropping SOONER (fall per foot traveled) in cold air vs. dense air, but I don't really agree with how he said it...

Bullets don't drop FASTER (per time) in cold air than hot, they just don't fly as fast so they drop SOONER (per distance traveled)...Meaning, the rate of fall isn't any FASTER, it's just that they don't travel as far horizontally per second as they would in less resistive hot air...The rate of fall is constant, the gravitational constant, 32.174ft/s.

Truth be told, the rate of fall would be SLOWER in cold air than hot (miniscule amounts) because of the density change...the more dense the air, the more bouyant force it exerts on the bullet...but this is a very small change, so it is over shadowed by the huge increase in drag force which slows the bullet and makes it fall sooner (in feet).

People miscommunicate that because they see their groups hitting lower at 100yrds in December than they did in June...they assume this means their bullet is dropping faster, but this is impossible, since the gravitational constant is a CONSTANT.

It's like the figure Bilge posted earlier, the dropped bullet and the fired bullet---no matter the speed--hit the ground at the same time.....it's just that the bullet in cold air isn't going to fly as far as the bullet in hot air.

Which I'd imagine is often also exaggerated by the fact that many modern powders are temperature sensitive, and will burn more efficiently at higher temps (giving higher pressure and muzzle velocity)...so you've got less resistive air and higher muzzle velocity, cold air shooting sucks.

RE: Bullet "Rise" - Dispell the Myth
 

If the guy at the gun shop is reading this, he's scratching his head and going "huh?":D:D:D. He's talking about the picture on the back of the old boxes of shotgun slugs and trying to justify that it's really what the bullet does.

RE: Bullet "Rise" - Dispell the Myth
 

This is very interesting stuff, thanks for the good responses even if I don’t understand some of it (physics was not my forte in college).

If I know anyone needing a PhD thesis in aerodynamic engineering, I will revert him or her to this post.

One question I have is from a post above. Someone was saying that a bullet drops faster in cold weather versus warm weather due to the density of the cold air. Why would the air temperature affect this if gravity is pushing down at a constant? An example would help to clarify this if at all possible.

RE: Bullet "Rise" - Dispell the Myth
 

If you are using Barnes X bullets, you will not have to worry about any of these things. X bullets defy all laws of physics - especially if fired from a Weatherby Vanguard.

RE: Bullet "Rise" - Dispell the Myth
 

Air density affects the bullet path independant of gravity. You would need a super computer to try to figure where a bullet would travel in real conditions. You have different air densitys, wind speed, wind directions, bullet rotation speed, bullet velosity and more along the path of a bullet. The only constant is gravity down at 9.8meters per second. So gravity is only one of the many forces acting on the bullets path.

If you can find a vacuum to shoot in. Your bullet will drop 9.8 meters per second directly straight in front of the direction the barrel was pointed when fired.

RE: Bullet "Rise" - Dispell the Myth
 

Bmullin, you haven't been watching this thread long aparently!!!

9.81m/s is pretty accurate even for air, unless you're talking a LONG fall, at which point a terminal velocity might be approached or reached...the fall of a bullet SHOULDN'T be in that category.

Joe D. Check out my last post before this one re: the air density/bullet fall relationship

RE: Bullet "Rise" - Dispell the Myth
 

Nomercy
I was just trying to answer the one question. I was just saying gravity is independant of everything else. And is constant.

A bullet would actually fall slower in dense air because of resistance. But the trajectory would drop off faster because the velocity would be slowed faster also.

RE: Bullet "Rise" - Dispell the Myth
 

Guys, no need for a super computer. Throw this into bernoullis equations in a intregal equation over time for dynamic Bullistic Coef, mix in Newtons third law of motion, throw in more of bernoullis for average turbulance, and your done.

RE: Bullet "Rise" - Dispell the Myth
 

or you could buy 300 bullets and 300 targets and set up a target every foot for one hundred yards and trace the point of impact. Either that or try to catch the bullet on film and slow it down.

RE: Bullet "Rise" - Dispell the Myth
 

When ever I hear someone who is "miss informed" about something (particualrly hunting/shooting) I try to educate them. 1. it will help them out 2. it may stop them from "miss informing" others. Walking away to hit my head against a wall will not do anything posative for anyone.

"A picture is worth a thousand words" really applies to explaining the path of a bullet in this situation.

The line of sight
The line of the barrel
The path of the bullet

drawn on a scrap of paper helps a lot to explain the "bullet rise" and also to show the big advantage a .270 has over a 30/03 when shooting at deer at longer ranges.

Robin