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In my not-so-humble opinion, unless both the distance and the angle are extreme, the variation is probably going to be less than the typical rifle shooter's "wobble factor".

RoyGBiv wrote:The effect of gravity will change with altitude, but not measurably if the change in altitude is only 15 feet (or even 100 feet). Actually, there is a change, but you'd need some high-falootin instrumentation to measure it and it's not enough to affect your aim point over a distance of 150 yards.

I'm not sure altitude-induced differences in gravity matter at 1,500 yards. I'm no ballistics expert, but I bet the air density of different altitudes affects trajectory more than the change in gravity.

To make this simple go online find a ballistic calculator enter in the data points and do what it says The one I found for Android is called Strelok it is free. Sorry just to lazy for all that math.

We're also going to need some latitude and shot direction info to do some Coriolis calculations.

texasmusic wrote:We're also going to need some latitude and shot direction info to do some Coriolis calculations.

Your bullet's got to have some serious hang-time for that to matter...

Who says gun nuts are dumb rednecks? Trig...nuff said.

If you start with a flat 200-yard shot, then go up a 15 foot tree stand, (assuming the stand is straight, not crooked) the horizontal distance is still exactly 200 yards, so the bullet will drop the same over that distance, within measurable parameters, even though the bullet will travel fractionally farther to reach the target.

Calculation....
Distance 200 yard shot.
Elevation 5 yards (15 feet)
Horizontal distance will remain 200 yards, but the bullet will travel a total of (a-squared + b-squared = c-squared) (200*200) + (3*3) = Square root of 40,009 = 200.0225 yards.... an extra .0225 yards = 0.81 inches of travel, but still the same horizontal distance.

The bullet will have lost some extra energy (0.81 x effect of drag per inch of travel) vs the flat shot.

If the elevation change is more pronounced, say 120 feet (40 yards) of elevation if you're shooting down a hill, the horizontal distance is still 200 yards, although to your eye it will seem a bit farther.... You may perceive the shot to be 203.96 yards (because you're using a laser finder, of course), which is the distance the bullet will actually travel (the length of the hypotenuse). About 12 feet more than the horizontal distance.

Now I need a beer to cool the embers of my 10th grade brain.

UGGGGGG..... don't try reading this before your first cup of coffee..... I'll be back this evening to finish up!

AndyC wrote:

Jumping Frog wrote:

AndyC wrote:You calculate drop over the horizontal distance - calculate the true horizontal distance (because gravity affects bullets only straight down) using cosine tables

This is a good approximation, but it is not the complete answer.

No, it's a pretty accurate rule of thumb called the Rifleman's Rule and is accepted in the sniper community world-wide;

Since you have obviously thought about this topic, you may be interested in an article called "Incline Shooting" in the current (Jan 12) issue of GUNS magazine (page 52).

Digital edition available here (free but requires an email address): http://fmgpublications.ipaperus.com/FMG ... /GUNS0112/" onclick="window.open(this.href);return false;

The article addresses the cosign method first. Using a classic .308 Winchester target load with 100 yard zero, the horizontal elevation adjustment needed at 500 yards is 63.3". At a 40 degree incline -- which calculates to a 383 yard horizontal distance -- a 31.1" adjustment is calculated. The exact elevation adjustment needed for a 40 degree angle shot at 500 yards is 43.6". Thus, the error using the cosign method ("Rifleman's Rule") is 31.1 - 43.6 = -12.5". Not too good if you are trying to make a hit on an 8" kill zone.

It concludes:

This method is correct in reducing the effective distance to the target. However, the bullet will spend just as much time getting to a 500-yard target at 40 degrees as it will getting to a target that is horizontal. That is because gravity pulls the bullet's trajectory over 500 yards, not 383 yards. The ... drop value is based primarily on the gravitational force over the time of flight.

The second rule of thumb method uses MOA instead of inches. Subtract 1 MOA for every 20 degrees. A 500 yard horizontal shot takes a dial comeup of 12 MOA from a 100 yard zero. Using this method, the hunter looks at the chart, see 12 MOA, and then subtracts 2 MOA for the 40 degrees (1 MOA per 20 degrees). The end result is a 10 MOA comeup. However, the true correction for 500 yards is to comeup 8.5 MOA. A 1.5 MOA error at 500 yards translates to a 7" error, so the result is slightly better than the cosign approach.

A better approximation was developed at Perry-Systems It basically multiplies the horizontal comeups (for the actual target distance) by the cosine of the incline angle and subtract a bias value. This method takes the actual time of flight into account.

And here I was expecting an answer involving monkeys hanging from tree branches and letting go at the moment the bullet is fired.

All this ballistics talk makes me want to get back into NRA High Power Rifle.

Jumping Frog wrote:

.... because gravity pulls the bullet's trajectory over 500 yards, not 383 yards. The ... drop value is based primarily on the gravitational force over the time of flight.

Makes sense... Thanks.!
The OP was asking about shooting from a tree stand with (assumed) 15 foot elevation above horizontal... KISS method applied to response.

The easier math is a squared + b squared = c squared. A being your height and B being straight line distance from grade to target. So if you were 200 yards at grade and 20 yards above the target the line of sight distance would be 200x200 + 20x20 or 40,000 + 400 = sight distance of the square root of 40,400 which is 200.99 yards. You have to be way above the target to make a real distance.