Correct me if I am wrong Bit, it sounds like you are trying to say that the + or - that we see in ballistic charts are the height of the bullet in relation to the muzzle as a horizonal line. If so that is true however the degree that the muzzle must be elevated in relation to this horizonal line is directly related to the LINE OF SIGHT.

In order to defeat gravity the muzzle of the weapon must be elevated on the weapons center axis so as to toss the projectile at an "arch" so that it will cover the sighted in distance and intersect with the aiming point before gravity, which is constant, drags it to the ground. This can cause the projectile to actually start out below the line of sight and cross that line of sight and hit the aiming point when it falls back to earth and intersects with the line of sight again, which is, hopefully, your aiming point. The key word or phrase is gravity is constant. From the time the projectile clears the barrel it is being pulled to the ground at a constant rate.

Now knowing that your barrel is already elevated it makes sense that if you are shooting uphill then that elevation becomes even more great and can result in a shot that misses high. Works the same downhill. As Bit says "aim low". Shoot uphill and you are over-compensating for gravity, shoot downhill and you will help gravity with thousands of feet per second, hence the bullet never attempts to "drop" there by causing a shot that misses high.

Its all about "line of sight vs distance, Velocity and mass" that determines how much positive elevation the muzzle must have to provide the correct "arch" needed to defeat gravity and create a satisfactory intersect with the aiming point.
I think!! ?

Perhaps there are different charts out there but charts I've seen are relative to the LOS. LOS being the line defined by the point in your scope and the point you wish to impact on the target. This is why the charts usually start "-" because the muzzle is a inch or two below your scope. Goes +++++ for awhile then a 0 then ------.... The reason it does that is for exactly the reason you said, the muzzle is slightly elevated and not parallel to the LOS.

Val and others are correct about the 100 yards on an angle (up/down) having a shorter "horizontal" run (as defined by the equation given above) and this accounts for most of the higher impact compared to a no-angle shot, because gravity has less time to does its dirty work.

However, I was just nit picking and mentioning that this is not the entire reason that it impacts higher. Some of that extra height gain is because of altering the relationship between initial Vx Vy of the bullet and the downward gravity force (Gy). As the shot angle increases, your contributing more of what was Vx to what is now Vy, directly opposed to the downward gravity force.

As a simple demonstration of this consider that in order to sight in your rifle the muzzle is tilted up two degrees above the parallel. Then if you make a 88 (nearly straight up in the air, the 88 degrees being between the parallel and the LOS) degree shot, the bullet is going to go straight up and come down nearly right on top of you. This is for all practical purposes (ignoring wind turbulence) a flat shot. So your once parabolic "arched" flight path at 0 degrees has been perfectly (or as near as it is going to get to perfect) straightened out at 88 degrees.

For low angles and short distances, this second effect is minor, especially for fast projectiles. So in practices you can just ignore everything I've said. I was just throwing it out there to be complete.

After reading what I typed I see that I did infact say charts are from muzzle when I meant to say LOS, sorry my typo.
I also would like to point out that mass makes no difference in gravity, all mass has equal pull by gravity. What mass does do is reduce velocity which is what is used to temporarily defeat gravity.

Does this apply south of the equator also? :-?

And of course.....none of this applies to a .270 when shooting at Elk!!

OF COURSE NOT!!! DUH - a .270, while behaving as a regular caliber when shooting at all other types of game, does, in fact, become a veritable laser when fired at elk. Impossible to miss, no kick, and extremely lethal.

LOL

Jesse Ostler

Horizontal Distance is What Matters
By now, most people understand that gravity only affects the horizontal component of a bullet's path--whether or not you are shooting uphill or downhill. The steeper the shooting angle becomes, the less the horizontal component of the angle becomes, and the less chance gravity has to "curve" or "arc" a bullet's path. The examples below illustrate the horizontal components of an uphill or downhill shot:

The less chance gravity has to affect your bullet (i.e. less horizontal distance traveled), the flatter your trajectory becomes. In other words, your bullet's path is closer to where you barrel is actually pointed.

By now you might be thinking, "Ok, so at 500 yards at a 60-degree angle, my bullet is affected by gravity just the same as 250 yards on flat ground, so I would aim like it was a level 250 yard shot, right?" WRONG! This is the a myth in uphill/downhill shooting. The reason is very simple. Forget about gravity for a moment, remember, you are actually shooting at 500 yards and your barrel is pointed much higher from your line of sight at 500 yards than 250 yards.

In order to accurately compute the uphill/downhill trajectory, we must factor in BOTH the shot angle and the barrel-scope relationship.

Putting it All Together
Now that we understand the factors of angle shooting, how do we figure out the numbers for our individual gun, load, and zero? The answer: A ballistics program that computes uphill-downhill bullet paths at different angles. There is no other way. You can either purchase custom made cards for your particular load (check out http://www.ballisticards.com) or, if you have a computer, you can purchase a ballistics program. Sierra Bullet's Infinity ballistic program is excellent for this purpose. Be careful, as some other programs will give you the angle measurement is Minutes-of-Angle (MOA), and the only way you can use that data is to manually adjust the dials on your scope. The way you use a ballistic program is to set up the load and zero parameters for level ground, then see how the trajectory looks at different angles, keeping those same load and zero settings. Once you run all the numbers, you need to make a "cheat sheet" and keep it with you in the field.

Excellent diagram.

If you get the data in moa you simply have to multiply it to use it as inches. Very simple math. In case you don't want to use your scope knobs.

For most shots, out to 500 yards and most normal angles involved, calculating in scope height, time of flight, barometric pressure, temperature, and altitude, all of these won't combine to amount to a miss.

Once you get further out you have to consider all those factors. Not just what the program tells you.

AND you have to shoot your rifle a lot. Because its not uncommon for Leupolds or other scopes to advertise quarter moa clicks and actually have a value of a third or fifth per click.

The point about pointing your barrel much higher on an uphill shot- how does that come into play for a downhill shot? I think I know what you mean, but when shooting downhill the components for the shot are the same except you are pointing downhill. Not up high.

Anyway FWIW those short shots out to 500 or less-- just use horizontal, its good enough.

I did the calculations on my 338. The shot was 802 yards slope distance. But the calculated horizontal distance was just over 600 yards. So I held with the 600 yard hold and dropped 2 in perfect.

Jeff

Shooting Uphill and Downhill:
What You Need to Know

Although many people don't realize it, shooting at an upward or downward angle will cause the bullet to impact higher than expected. For example, if you're shooting downhill at a 30-degree angle and your laser rangefinder says it's 400yds, you cannot use your 400yd elevation settings or the bullet will impact too high.

The actual range isn't what's important when making elevation adjustments, it's the horizontal range that's important. This sounds strange to many people, but there are fairly simple physics involved. However, knowing why it happens isn't really of any use to the average hunter or shooter, the only important thing is to know that this occurs.

So, how do you figure out what elevation setting to use? Well, you have to determine the horizontal range and use the horizontal range to determine what elevation settings are needed. Fortunately there's a fairly simple formula to determine the horizontal range.

Slope Range X COS of Angle = Horizontal Range

Degree of Angle COS of Angle
10 .98
20 .94
30 .85
40 .75
50 .65
60 .5
70 .35
80 .2
90 0

Here's some examples...

The measured slope range is 200yds and the angle is 20-degrees. 200 X .94 = 188 So the horizontal range is 188yds, and you adjust your elevation for a 188yd shot.

The measured slope range is 600yds and the angle is 30 degrees. 600 X .85 = 510 So the horizontal range is 510yds, and you adjust the elevation for a 510yd shot.

As you can see, the farther the range and the steeper the angle, the more difference it makes. If you're taking a 100yd shot and the angle is 10-degrees, then it really isn't going to matter. However, as the range increases and/or the angles get steeper, you'll definitely need to make corrections.

NOTE: This formula only applies to elevation adjustments.

Not to be a spoil sport or seem like a now-it-all, but there are many misconceptions being thrown around about the physics involved here. The main thing to remember is that you aim higher whether shooting up or downhill, and while there may be formulas to give you an idea of how much higher to aim, in reality it is like any other type of shooting. It just takes PRACTICE!

But hey part of being a hunter is being able to sit around the fire and talk smart with your pals so keep at it!!

At that campfire we are sitting around enjoying, exactly what are we burning?

Just curiuos if it causes us to think we have to aim higher?

Jeff

Pakalolo...

Shaka bud has the ability to produce a sensation that everything and everyone should be a little higher.... Up hill or down hill just aim higher.... It's all good....

Now excuse me while I statisfy this weird - urgent craving for more brownies...