Shooting downhill???

[DLH]

Is there some place that I can findout how much a bullet will drop or rise from point of aim, when shooting down hill. (or I should say mountain)

[SDS-GEN]

The Pythagorean theorum (Asquared+Bsquared=Csquared)will tell you what your straight line distance to target is.  Straight line distance(parallel to gravity) is where bullet drop is determined.

[Graybeard]

Is there some place that I can findout how much a bullet will drop or rise from point of aim, when shooting down hill. (or I should say mountain)

Basically the answer is no.

There are now several rangefinders that have a feature to tell you the true distance to a target at a steep angle to you. You can then use that distance rather than the linear distance up or down slope to use in aiming. You still have to know the trajectory of your bullet.

The thing to realize is that if the angle is gentle and the distance isn't great ignore it. If the distance is long and the angle is steep it's always less than it appears or a standard rangefinder will indicate. Figuring the how much less out in the field other than with one of the newer ARC rangefinders is at best pure guesswork. Luckily most modern rifles shoot flat enough that inside normal shooting distances for most of us it's not all that important.

If your angle is over 30 degrees and distance over 300 yards tho it does make a lot of difference.

[IOWA DON]

I think Sierra sells a ballistics calculation program which will gives that information in the output. However, I got a video about long range shooting (for hunting), and in the video they said that for the most part when shooting uphill or downhill that any compensation could be neglected. The first reason was that on big game size targets the compensation, even for very steep inclines and normal ranges, would be small compared to the size of the target. The second reason was that for very long ranges, the angle of incline is rarley very steep. Another factor in regard to shooting in the mountains is the altitude. That is, if one has sighted in their rifle at a much lower elevation and knows the trajectory of the load at that lower elevation, it will shoot flatter at a higher elevations because of the thinner air not slowing the bullet down as quickly. I went antelope hunting last year in Wyoming where the altitude was between 5,000 and 10,000 feet. I took my .338-.378 Weatherby which is set up for long range shooting with a long heavy barrel and a scope with a custom range compensating reticle. It shoots a 225-grain Nosler Accubond bullet, which has a pretty good balistic coeficient at 3,330 fps. On my old ballistics program I compared trajectories at 1,000, 6,000, and 11,000 above feet above sea level. In short there was barely an inch of difference at 400 yards for the different elevations, but much more at longer distances. For example, going from 1,000 feet to 6,000 feet elevation for a range of 600 yards the bullet drops 3 inches less. And going from 1,000 feet to 11,000 feet elevation for a range of 600 yards the bullet drops 7 inches less. That amount would be significant on a deer or antelope. For a rifle with a cartridge with less velocity and a bullet with a lower ballistic coeficient I would think that varying the elevation would cause a greater difference in trajectory.

[corbanzo]

It is the exact same as uphill.  All that matters is the difference in degrees from horizontal.  If you have an arc rangefinder, it will tell you the correct horizontal difference whether it is uphill or downhill.  Some new rangefinders have ballistic information in them to tell you the correct bullet drop at that distance also, you just have to set the rangefinder to your firearms ballistic characteristics. 

SDS_GEN is exactly correct with the pythagorean theorum.  But knowing that is almost impossible, you can get C using a rangefinder, but knowing B to get A is that impossible part.  Now if you have a scientific calculator, you can use a rangefinder to get your C distance, use an angle measurement tool to measure the angle of the slope, and use the arctangent function of the calculator (C*Arctan(Angle)) I believe and it will give you the A distance, or the horizontal distance to base your bullet drop on. 

Even with this information, as GB stated you need to know your bullet drop at that distance, which you can get through having a range card with you, knowing your gun and having the drop memorized at certain intervals, or having a graphing calculator with the function of your bullet drop programmed into it. 


Or you can do what people have been doing for thousands of years, take a good educated guess. 

[SDS-GEN]

One mistake I made in my post, straight line distance should be perpendicular to gravity, not parallel to it.

[Dave in WV]

I remember reading an article written by Craig Boddington about a product used for getting the angle and using a range finder you can figure the actual distance perpendicular to gravity. An example is: if a deer is 200 yards down the mountanside below you and IF you were on the same horizontal plane the distance would be 45 yards the actual hold for the shot should be 45 yards. You would need to allow for shot placement.

[tangob5]

Made this chart for myself.  A little bit of trig. Chart holds true either up or downhill.

Angle      % of Range
10                  2
15                  3
20                  6
25                  9
30                 13
35                 18
40                 23
45                 29
50                 36
55                 43
60                 50
65                 58
70                 66
75                 74
80                 83
85                 91

[trotterlg]

Not sure I believe those numbers, it you shoot straight up or down there will only be one place that the bullet and scope agree with each other, (probably at about 70 yards).  After that point, the bullet will just go higher and higher from the point of aim (as viewed in the sights).  When getting close to 90 degrees like the 85 degree mark in the table, I think the numbers will just not compute like your chart says, the bullet is flying at a different angle than the sight picture is, (slightly up).  Larry

[bilmac]

Yes gob.

Either I misunderstand how to use your chart or it is backwards. At the very steep downward angle the percentage of the range would be the least. As an example, if you were looking downhill at 85 degrees, and your rangefinder said 400 yards, the actual horizontal distance would be much closed to .1 X 400 = 40 yards    than .9 x 400 = 360 yards

[dukkillr]

Unless his chart measures the angle from vertical?  Meaning that 90 would be completely flat and 0 would be straight up.

[tangob5]

Reduce the known range by the percentage.  If your shooting up or downhill at a 45 degree angle you reduce the range by 29 percent or multiply the range by .71.  I actually would reduce the range by 30% or multiply it by .70 because the math is easier on the brain and an extra 3 yards is not going to affect you much.  Range finder says 300 yards (unless you have a angle compensating one) shoot for 210 yards.  Sorry I did not explain it before.  It's easier for me to subtract the percentage from the range in my head so that's why I use it. 

[mrbigtexan]

i just aim at the bottom of their belly but keeping it on hair.

[mechanic]

Made this chart for myself.  A little bit of trig. Chart holds true either up or downhill.

Angle      % of Range
10                  2
15                  3
20                  6
25                  9
30                 13
35                 18
40                 23
45                 29
50                 36
55                 43
60                 50
65                 58
70                 66
75                 74
80                 83
85                 91

Ya'll makin my head hurt.  Sorta like golf.  If its uphill its really farther.  If its downhill its really closer?  Gotta go take a tylenol.

   

[trotterlg]

The flaw in these calculations is that they are calculated as if the scope and bore are pointed exactly parallel to each other.  In real life they are not parallel, the scope and bore intersect each other at some point, so, depending on the scope heigth above the bore, there will be an angle at which the bullet will never impact the point of aim in the scope no matter what the distance.  Larry

[tangob5]

You can get into a lot of technical discussion about the bullet drop either up or downhill, scope height etc.  Bottom line is when shooting up hill or down hill the bullet drops at the same rate as if shooting level.  Being almost technical if you have a right triangle the leg you would measure with a non-compensating range finder would be the hypotenuse call it "c".  You would have a vertical leg let's call it "a" and a horizontal leg called "b".  Now a Greek gentleman by the name of Pythagoras came up with an equation "a" squared + "b" squared = "c" squared.  When shooting up or down hill it is leg "b" we need to be shooting for.  Example: C= 500 yards, a = 300 yards then we shoot for "b" or 400yards.  Using trigonometry is much easier and that is what I used to make the chart.   

Here's a fun question.  If you had a bullet fired level at a MV of 3300 FPS and a bullet dropped by hand at the same height and at the same time which would hit the ground first? 

[epanzella]

The tricky part is getting an animal to hang around while you hash this out. While all said by everyone is technically accurate, in the real world it would take a pretty unusual situation for the angle to matter. As the angle gets steeper it becomes less and less likely that an animal is far enough away to make a practical difference in your hold. With modern flat shooting guns less than 45 deg and less than 300 yds (horizontal distance) the change would be small. In bow hunting, of course, angle makes a substantial difference. 

[bilmac]

There we go, the practical answer.