kevin c Posted August 16, 2003 Share Posted August 16, 2003 Reading the new (48th) ed. of Lymans, looking at the exterior ballistics section. To paraphrase: the point of impact shifts up when shooting up or downhill because the distance travelled by the bullet over the true horizontal (perpendicular to the earth's core/direction of the force of gravity) is less than the distance sighted for. IOW, if the range is the hypoteneuse of a right triangle, the legs being shorter, the bullet travels for a shorter distance under the effect of gravity and therefore doesn't drop as much as it would as in sighting in over the same distance with no angle up or down. What the hey? This isn't right, right ? Link to comment Share on other sites More sharing options...
George Posted August 16, 2003 Share Posted August 16, 2003 It is right. Flatter (slightly) uphill & downhill. A good ballistic program will allow this to be calculated. Regards, Link to comment Share on other sites More sharing options...
EricW Posted August 16, 2003 Share Posted August 16, 2003 It is correct. There will be less and less drop as the angle of the muzzle approaches +/- 90 degress from the horizontal. Think about it: at 90 degrees, there must be zero drop, since the bullet is travelling in the same direction or directly opposite the force of gravity. The simple rule is that whenever you are shooting up or down a grade - your bullet will strike high. Make sense now? Link to comment Share on other sites More sharing options...
cpty1 Posted August 16, 2003 Share Posted August 16, 2003 Someone told me years ago that when firing either up or downhill to aim low. Seemed to me back then if you aimed high for one scenario, then you'd need to aim low for the other; shouldn't be the same for both. However, it don't work that way. I've tested the theory repeatedly when shooting shotguns, mostly duck and dove hunting. While I never worried myself with the physic or ballistic reasons, I can tell you it's true. The greater the angle, either up or down, the lower you need to aim. Link to comment Share on other sites More sharing options...
echo3mike Posted August 16, 2003 Share Posted August 16, 2003 I posted a thread on The High Road about angle fire. For most shooting it's not as much of a factor as wind, temp and baro pressure. Only when the distances and/or the angle are extreme does the need for correction occur. The most effective sight correction method at any range / angle is Slope range scope adjustment (in MOA) X (cos slope angle) = corrected scope adjustment (in MOA). Another post has Sierra's latest offering about angle fire. Hope this helps. Scott Link to comment Share on other sites More sharing options...
John Dunn Posted August 16, 2003 Share Posted August 16, 2003 Kevin C, I too have heard multiple confusing explanations for angle shooting. The links above do a good job explaining it. The thing that always confused me is that most people when explaining the problem say crap like, "Gravity only works over the horizontal distance to the target." Which we know is BS, as gravity is time dependent and will pull a bullet down the same amount whenever the time of flight is the same. The essential difference being that with angle shooting, gravity isn't pulling the bullet down perpendicular to the line of sight. Can't tell you how many times I've heard that gravity only works on the horizontal, even in gun rags. Always made me wonder what planet these guys grew up on. Link to comment Share on other sites More sharing options...
BigDave Posted August 16, 2003 Share Posted August 16, 2003 This is a common thing in 3D archery and IFAA field archery. Up or down, hold low. Its very easy to see with an arrow going 270 FPS. Link to comment Share on other sites More sharing options...
rkgsmith Posted August 16, 2003 Share Posted August 16, 2003 Not to piss some people off but gravity knows no difference, and acts only on a horizontal plane. The most common cause of missed shots is due largely to a misjudgement in range by the shooter. Think of it this way. You are standing at the base of a 15 story building, and your target is 100 yards away, your zero is 100 yards. Now go up to the top floor and the distance to the target is now 135 yards. However, once the round is fired it is only being acted upon by the forces of gravity for the 100 yard distance. If you dial for 135 yards you will indeed shoot high. If you want to think of it in terms of distance visualize two mountain peaks, 300 yards apart, You on one side, and your target on the other. If you walk down one and up the other you may have to cover 1000 yards, but the distance between you and the target is still only 300 yards. Range estimation is the true key to accurate hits at angles. Link to comment Share on other sites More sharing options...
John Dunn Posted August 16, 2003 Share Posted August 16, 2003 Rkgsmith, However, once the round is fired it is only being acted upon by the forces of gravity for the 100 yard distance. Respectfully, wrongo. Gravity will act on the bullet over the entire time of flight to the target. It will take longer for the bullet to cover 135 yds than 100 yds. The difference is that in level shots gravity is pulling essentially perpendicular (vertically) to the line of sight, and with angled shots it is not. If you are using a laser range finder or mil-dots for your range estimation, you are going to get the actual distance from your target, not the horizontal distance. Take this number and apply one of the formulas or use the quick and dirty read off a Mil-dot Master and make the compensation. Not to piss some people off but gravity knows no difference, and acts only on a horizontal plane. So you are saying that a bullet fired vertically is not affected by gravity? Not true. A better statement would be to say, "Pretend that gravity only works across the horizontal distance to the target when determining your holds for angled shots, remembering that the reality is that gravity is always on. Your explanation is the one I've always heard, and it is untrue, but it will help make the right compensation for hits. This is probably why the myth continues. Not trying to start a fight, but couldn't let the wrongness of your post infect others! Link to comment Share on other sites More sharing options...
Flexmoney Posted August 17, 2003 Share Posted August 17, 2003 You all are saying the same thing and don't know it. (And, yes...I find that funny.) Link to comment Share on other sites More sharing options...
EricW Posted August 17, 2003 Share Posted August 17, 2003 You all are saying the same thing and don't know it. (And, yes...I find that funny.) Close, but not quite, some answers are incorrect. John Dunn has it closer than anybody. The best visual description of how this works is done using vector decompositon. If I get some time, I'll post a pictogram showing how it's done. The math is no more than simple trigonometry. This would make a great physics lab experiment. At least it'd be a damned sight more interesting than the typical acceleration of gravity experiment. Link to comment Share on other sites More sharing options...
John Dunn Posted August 17, 2003 Share Posted August 17, 2003 Flex, We are saying close to the same thing. Always happy to be a source of amusement, though. Tomorrow I'll post how many Angels can dance on the head of a pin EricW, the diagrams in the Sierra link above are pretty good. Link to comment Share on other sites More sharing options...
EricW Posted August 17, 2003 Share Posted August 17, 2003 Tomorrow I'll post how many Angels can dance on the head of a pin Woohoo!! At least we'll get one connundrum of the ages resolved. EricW, the diagrams in the Sierra link above are pretty good. I looked at the exteriorballistics.com diatribe. Talk about making something very simple overly complicated... It's just not that complex of a problem. And there is only one correct answer. One picture and a few lines of equations are all it takes. Sigh... Link to comment Share on other sites More sharing options...
George Posted August 17, 2003 Share Posted August 17, 2003 But really folks, the distance across the gravity well is the same, it's just that we are not using the same force across distance frame to measure things. We are getting more distance covered while in the same gravity gap when at an angle other than 90 degrees to the force in question. It can be argued that the time gravity is applied to the object is less, or it can be argued that the force of gravity applied is less per unit of distance (90 degrees across the well) travelled versus time to transit said distance. It can also be argued that we are spending the same time in less gravity. The key variables are transposable here so a number of ways of viewing this are correct if the end result is all we care about. The fact of the matter is that there is a force application reduction in the perpidicular axis involved whenever you are not at an exact right angle to the application of the side force. The reduction is achieved by adding some of the side force to the forward motion (accelerating) of the projectile while going downhill, and pushing against (decelerating) the projectiles forward motion when going uphill. We are just looking at a vector here. Regards, Link to comment Share on other sites More sharing options...
Steve Anderson Posted August 17, 2003 Share Posted August 17, 2003 simple trigonometry? If ever there was an oxymoron.... SA Link to comment Share on other sites More sharing options...
George Posted August 17, 2003 Share Posted August 17, 2003 Here is a PDF from MIT that sheds light on the vector method of looking at this type of thing. Review 1b.pdf The earlier posts about true flight distance are absolutely correct about the line of sight distance to the target being the correct ballistic solution. Offsets only need to be figured if you use a 2D map type distance to an object substantially above or below your starting vertical plane of reference. Regards, Link to comment Share on other sites More sharing options...
John Dunn Posted August 17, 2003 Share Posted August 17, 2003 It can be argued that the time gravity is applied to the object is less, or it can be argued that the force of gravity applied is less per unit of distance (90 degrees across the well) travelled. It can also be argued that we are spending the same time in less gravity. The variables are transposable here so a number of ways of viewing this are correct. Dude, Earth's gravity is a constant (32ft/sec/sec) acceleration. The time of flight is determined by the velocity and the direct distance to the target. For the time gravity is applied to the object to be less, the time of flight would have to be less, which means your bullets would have to have a higher muzzle velocity when fired on an angle. It doesn't work this way. or it can be argued that the force of gravity applied is less per unit of distance (90 degrees across the well) travelled. Once again, gravity is a constant. Whether fired at a angle or horizontally, each bullet will fall the same amount in the same amount of given time. It can also be argued that we are spending the same time in less gravity. I have never felt gravity lighten up while shooting on an angle! EricW, a little help here please. We are just looking at a vector here. Now that I agree with ! Link to comment Share on other sites More sharing options...
Liota Posted August 17, 2003 Share Posted August 17, 2003 Trigonometry in shooting too? Thought I left that all behind me in high school and college. Liota Link to comment Share on other sites More sharing options...
Sam Posted August 18, 2003 Share Posted August 18, 2003 I agree with Steve! Simple trigonometery is an oxymoron. I was blessed at birth with very high brain density. Basically, that means you only have to hit me over the head with the truth about a dozen times before I "get it". But, when I finally "get it", I've "got it". But, I don't have time for that now....... So, hypothetically speaking, if I am shooting at an 8" round gong and my rangefinder read "400 yds", and my amazingly keen sense of observation reveals to me that I am also about 250 feet higher than the gong. Do I just dial my scope to the 400 yard setting and bust that puppy in the middle? BTW, this is what I have been doing at 400 yards and 60 feet of elevation difference between high and low positions and if there is a difference on an 8" gong I haven't been able to tell it. Or should I hold "just a tad low" from a much higher position, like in the lower 1/3 of the gong? I really like emperical evidence, theory makes me sleepy. Please keep it mercifully simple, Signed, Dense and desperate How many angels can dance on the head of a pin? That's a piece of cake! Matthew 19:24-26. Link to comment Share on other sites More sharing options...
echo3mike Posted August 18, 2003 Share Posted August 18, 2003 At the shorter ranges and/or smaller angles, it's not that important. For your scenario, a 400 yd slope range and an ele difference of 250 ft / 83.33 yds equals a horizontal range of 391yds. Even if both the slope range and elevation were doubled, the horizontal range would be close to the slope range...The angle must be extreme (>25 degrees or so) for it to have any impact on sight adjustments and POI. I've heard most of the explainations trying to account for the condition and I really couldn't give a rats FFA about why it happens. The "big dogs" have bigger sheepskins than I do and more time and money to figure this out... and it's still irrelevent. What's important here is knowing how to shoot the condition, how to hit the target. Personally I'll wait until a solid, concrete series of data sets is collected before I pin my belief system into a single hypothesis, and pay more attention to things like windage and temp than the rare extreme angle shot. FWIW, Scott Link to comment Share on other sites More sharing options...
Larry White Posted August 18, 2003 Share Posted August 18, 2003 Granddaddy said estimate the range, then shoot less high. Always seemed to work for him and he shot a 44/40 up and down some pretty good hills. Larry Link to comment Share on other sites More sharing options...
kevin c Posted August 18, 2003 Author Share Posted August 18, 2003 Thank you all, for your comments, esp. John Dunn. Yes, I knew that you'll shoot high aiming up/downhill, but the explanation in the new Lyman's didn't jive with what I thought I knew about physics, and, furthermore, didn't jive with the explanation given in the previous addition of Lyman's (which, by the way, goes with what John said). Link to comment Share on other sites More sharing options...
George Posted August 18, 2003 Share Posted August 18, 2003 Truth be said, everything but the vector analysis reference section of my earliest post was me funnin' with this a little and some of what follows is still in a tone of jest, I will be more obvious about it this time around. So hmmm, let's see now, we are getting equal projectile deflection/drop for supposedly more time of force applied while traversing the gravity well on a slightly longer path during angle fire eh. Something in the big 3 (force, time, distance) has to slip for the result to work out unless things aren't equal in the time or force departments. If the force is being applied as a vector, then the energy not used to increase drop should be getting applied to increasing speed and maybe this is enough to account for the flight time being the same across the slightly longer distance when the object is travelling in a complementary direction to gravity (downhill). When shooting uphill the gravitational pull contributes deceleration to the projectile and the required acceleration isn't being added there, so I hypothesize (just for fun of course) that since the force of gravity is decreasing just the tiniest amount as the altitude increases, acceleration is imparted by a lessening of gravity due to the increasing distance from the source of that gravity. Hmmm, does this mean that on the downhill flight the rate of acceleration is accelerating and that on the uphill flight it is not but flight time is still equal between the two types of angle fire, or is it? Of course a vacuum across the projectile flight path would be needed for an accurate test here because the effects of air are of greater magnitude than what we are trying to measure if we are really trying to verify that time equals distance divided by money :-) Everything up to here is in serious jest, just because it's funny how stuff is, or is it how funny stuff is? Now back to reality, Time of Flight = Drop, and Vector Analysis will plot this, and that is indeed all she wrote. Yessiree, the slope has to be extreme for the path to vary much so mostly this is moot unless you are shooting at an object (exagerated example) 400 yards away, and 400 yards below or above you. I have never corrected for this because I have never shot a rifle at anything over 10-15 degrees up or down from horizontal at more than 300-400 yards in any competition or practice I have done. I hold right where I figure for flat and am done with it. The differences are truly miniscule enough to be immeasurable compared to all of the other factors controlling long distance accuracy. This thread is mostly just about saying that there is a measurable, albeit extremely small change in things that needs a better explanation but (almost always) won't mean anything in application. My apologies for twisting things up around here, but there is a bit of contradictory logic at work with this one and I was having a bit of fun with it. Regards, Link to comment Share on other sites More sharing options...
EricW Posted August 18, 2003 Share Posted August 18, 2003 Angel Count Update: 6.9862x10^32 +2 Link to comment Share on other sites More sharing options...
John Dunn Posted August 18, 2003 Share Posted August 18, 2003 Angel count: 42 George, glad you were funnin'. I was, like, concerned and stuff. Link to comment Share on other sites More sharing options...
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