Shooting at an incline or decline - Bullet trajectory

[crotalus]

So it's known that a bullet will drop past a certain yardage but what's a simple rule to remember when shooting downhill or uphill? I've read articles and seen pics of the trajectory curve but in the heat of the moment what is one rule to keep in mind?

[Coues 'n' Sheep]

I think it is much different with a rifle than a bow. In archery you can use the rule of thumb....90%,70%,50%.... It goes something like this: 30 deg. angle x 90%=shot distance, 45 deg. angle x 70%=shot distance, 60 deg. angle x 50%=shot distance. It does work. I don't think that will work with a gun..... so buy a range finder with a tilt compensator.

[hunter4life]

Basically what matters is the horizontal distance to the animal. So if it is 300 yards line of sight to the animal and it is either up or downhill, then the horizontal yardage is less and your bullet will hit like it is 260yards if the slope is 30degrees (212 yards for 45degrees) for example. As you can see at moderate distances with a moderate 30 degree slope, such as my example, with a fast shooting caliber you don't really need to adjust much at all.

 

Many people grossly overestimate slopes of hillsides. A hillside with a slope in the high 30's is very steep. The only time you will be shooting with slopes greater than that would be when there is a tall cliff somewhere between you and your target.

[Outdoor Writer]

So it's known that a bullet will drop past a certain yardage but what's a simple rule to remember when shooting downhill or uphill? I've read articles and seen pics of the trajectory curve but in the heat of the moment what is one rule to keep in mind?

 

Bullet drop is the same regardless of the angle of fire, because gravity works the same over the level distance only. So when you shoot up or downhill, the drop is based on the level-ground HORIZONTAL RANGE the bullet travels and NOT on the slanted distance traveled. As a result, bullets -- and arrows -- will strike high when shooting up or downhill if you sight for the actual distance of the SLANT range. Over short distances or at low angles, it's normally not an issue.

 

Hypothetical exaggerated situation:

 

If you're way up on a steep cliff 300 yards above a deer and shooting nearly straight down at the deer in a wash, your rangefinder will tell you the deer is 300 yards away. BUT...the horizontal distance would likely be less than 10 yards, which is the distance gravity would work on your bullet. So if your gun shoots 4" high at 10 yards on level ground, it will do the same for this shot. Obviously if you think it's 300 yards and adjust your hold to compensate, you will shoot even higher. -TONY

 

 

 

[Huntn coues]

So to make it simple alway's hold low up hill or down

[Red Rabbit]

A couple of reads. Seems that without a program, multiplying the bullet drop by the cosine of the angle would work reasonably well, better than multiplying the yardage by the cosine of the angle.

http://www.exteriorballistics.com/ebexplained/5th/33.cfm

http://www.longrangehunting.com/forums/f19...rections-22768/

[hunter4life]

Thanks, those were some good links RedRabbit. At long distances and steep angles a lot of factors must be taken into account, but at shorter ranges things can be very much simplified.

 

For me the take home points for shooting at game out to my comfortable range of 400 yards with a fairly fast cartridge (ie. 7mm mag) are:

1) Uphill or downhill have basically the same effect.

2) Using the horizontal range works fine out to 400 yards with a relatively fast rifle cartridge.

3) Out to 200 yards on a deer sized animal most of this doesn't even matter because a bullet hitting 2.5inches higher than expected due to a very steep 45degree angle should still be within the kill zone. The same can be said for 300 yards if the angle is 30 degrees or less.

[crotalus]

Some sweet info here guys, thanx. Here's why I asked. I shoot a .270 and twice I missed at downhill targets. One was a cow elk and another was a Coues buck. The elk was eventually taken but the shot was way high from where the "placement" was. The buck is just a "should/could of" memory. Both were steep angle shots, one in Unit 27 and the other from a cliff in 32. I made myself a promise not to do this again, so this info is great, but I don't know very many people who carry calculators in the field so "So to make it simple alway's hold low up hill or down" sounds like the rule. I was going to buy one of thos new fangled ARC rangefinders but heard and read some not so great reviews, so a regular rangefinder is in the pack now. Thanx again for all the great input, I know I could find some "shooting brainiacs" on here.

[.270]

if you shoot a .270 then don't worry about it. they don't drop. it's an anomaly of physics. only thing knowed to man to not be affected by gravity. that's why when you shoot a .270 you need to make sure you hit what you're shooting at. if you miss it keeps going until it hits something. i know a guy that shot hisself in the back o' the head. bullet went around the world when missed a bighorn. sad deal too.........Lark.

[Huntn coues]

You so funny lark

[bowhuntinmaniac]

Buy a Leupold RXIII......it has a inclieometer built in, one for bow, one for gun.

[shortpants]

Thanks, those were some good links RedRabbit. At long distances and steep angles a lot of factors must be taken into account, but at shorter ranges things can be very much simplified.

 

For me the take home points for shooting at game out to my comfortable range of 400 yards with a fairly fast cartridge (ie. 7mm mag) are:

1) Uphill or downhill have basically the same effect.

2) Using the horizontal range works fine out to 400 yards with a relatively fast rifle cartridge.

3) Out to 200 yards on a deer sized animal most of this doesn't even matter because a bullet hitting 2.5inches higher than expected due to a very steep 45degree angle should still be within the kill zone. The same can be said for 300 yards if the angle is 30 degrees or less.

 

Everybody should read this post and remember it. For most rifles, unless your shooting 400+ yards and at an angle of 30 degrees or more then it doesn't matter. 30 degrees is a lot steeper than most will ever have to worry about. I am one of those crazy people who carries a calculator in the cheek piece pocket on my rifle. I have an Angle Cosign Indicator on my scope and can calculate angle compensation while looking at my target. I have never used it in a hunting situation but I enjoy learning the ins' and outs' of long range shooting.

[25-06]

if you shoot a .270 then don't worry about it. they don't drop. it's an anomaly of physics. only thing knowed to man to not be affected by gravity. that's why when you shoot a .270 you need to make sure you hit what you're shooting at. if you miss it keeps going until it hits something. i know a guy that shot hisself in the back o' the head. bullet went around the world when missed a bighorn. sad deal too.........Lark.

Good one Lark

[Billinsd]

Great info. I just bought an angle cosine yesterday. Coues n Sheep, the 90% and others you mentioned in your post are the cosines of those angles, approximately.

 

The cosine of the angle is the side adjacent, horiz dist over the hypotenuse, the line of sight distance.

 

So, 90% would mean that the horiz distance is 90% of the line of sight distance.

 

Anyway the wife is calling me for lunch

 

Oh and it does not matter what the distance the cosine of the angle is always side adj over hyp.

 

Man, how nice is it to use something that was burned into my skull for something so fun as hunting. Man I love physics as applied to hunting situtations

 

Bill

[Hooked_on_Coues]

I really enjoy all this stuff but honestly I think for most hunting situations my Dad had the best advice:

 

"Don't shoot at it if you can't hold on hair."