Range finder & angle shots

[shakeyjake]

I think this fourm is the best place to get educated an answer. I'm new to range finders and just picked up a Nikon Riflehunter 1000. Seemed to work fine this morning and I'm happy with it. It can measure "line of site", or horizontal distance negating the incline/decline. So if there's a deer 180 yards away on a 30 degree incline it can measure actual distance or the distance if the deer is on level ground with you. Here's my question. Wouldn't I want "line of site" for shooting, so I know the actual distance the projectile has to travel?
I've done some target shooting out to 600 yards but never put any thought into angles.

 

[Caydel]

I think you might want to read up on http://en.wikipedia.org/wiki/Rifleman's_rule

 

[Haagen_Dazs]

My Bushnell rangefinder tells me line of sight distance and angle, then calculates the bullet drop.


Basically, if you're shooting either uphill or downhill, the bullet will drop LESS than a bullet shot a 0 degrees. This means if your scope maxes out at lets say 100moa, you can shoot (lets say) 1000 yards at 0 degrees, or about 1300 yards on an uphill or downhill slope.

 

[TV-PressPass]

The key thing with this angle thing is to realize that gravity only pushes in one direction:
straight down.

So when you range 400 yards on a mountain side, the diagonal IS the distance the bullet is travelling.

But it is only being affected by 375 yards of gravity, because its such a steep angle. So you should calculate your shot at 375 yards.

I have this fight with people all the time its kindof counter intuitive.

 

[shakeyjake]

The key thing with this angle thing is to realize that gravity only pushes in one direction:
straight down.

So when you range 400 yards on a mountain side, the diagonal IS the distance the bullet is travelling.

But it is only being affected by 375 yards of gravity, because its such a steep angle. So you should calculate your shot at 375 yards.

I have this fight with people all the time its kindof counter intuitive.

Basic laws of physics. I like your answer. I'll use the angle compensation thing on my range finder. I'll check out that Wiki link also.
Thanks

 

[Tcon]

A rangefinder that accomodates for the angles is very convenient if the range finder is accurate out to the ranges you are shooting. If you estimate range and calculate manually, enter values into ballistic software or use cards you can use a tool that attaches the rail to indicate cosine. The cosine indicator is very expensive but quick. A regular compass with inclinometer will work too on the cheap.

 

[Juster]

The cosine rule tells you that at 60 degrees at 600 yards just pretend it is 300 yards.
Which is right for straight lines, and therefore wrong for curved lines.
Type it into a ballistic calculator and see how far off you are.

Because:
Gravity is no longer operating at 90° to the bullet, so gravity does less (a fishing rod at 60° sags less than a horizontal one, OK?).
Your sights are higher than the bore, which changes the zeroing geometry.
The bullet takes twice as long to get there, and slows down.

So, you have to use a computer. A protractor won't do.

 

[Juster]

Some "experts" advise that when shooting on an incline, assume that the range to the target is reduced to its "horizontal component" or the horizontal distance to a plumb bob dropped from the target. Wrong!

What he said. longer to get there, more drop. Plus sighting geometry weirdness.

 

[AlexF]

Buy "Applied Ballistics for Long Range Shooting" for Christmas

Don't forget that when you shot at an angle part of the drop is perceived as an acceleration backward or forward which does not affect the angle between where you aim and where the bullet impacts.

This is non-intuitive and is why it seems that drop is less where you shot down or up but it is not since drop is proportional to the square of the time of the bullet flight!

You should get a copy of "Applied Ballistics for Long Range Shooting" by Brian Litz as a Christmas gift

Alex

 

[rnbra-shooter]

I think this fourm is the best place to get educated an answer. I'm new to range finders and just picked up a Nikon Riflehunter 1000. Seemed to work fine this morning and I'm happy with it. It can measure "line of site", or horizontal distance negating the incline/decline. So if there's a deer 180 yards away on a 30 degree incline it can measure actual distance or the distance if the deer is on level ground with you. Here's my question. Wouldn't I want "line of site" for shooting, so I know the actual distance the projectile has to travel?
I've done some target shooting out to 600 yards but never put any thought into angles.

A practical answer to the OP's question: just aim and shoot. Your sighted-in deer rifle (say, an inch or two high at 100) is going to hit, or miss, depending on how good a shot you are able to make under the circumstances. At that distance, the correction for range is meaninglessly small. And the correction for a 30 degree slope is also meaninglessly small.

Run the numbers through http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi if you'd like to explore this stuff. And if you are interested in learning about the reasons behind this, AlexF's recommendation of Applied Ballistics.... is a very good one.

Here's what I calculated:

bullet = 2700fps; scope set so that bullet strikes 1.8" above point of aim at 100 yards.

Shooting on the level results in the bullet striking 0.6" below point of aim on a deer 180 yards away.

Shooting uphill 30 degrees, your bullet will strike 2.1" high at 100 yards and 1.7" low at 180 yards.

So if you follow my advice of "just aim at your deer and shoot", the difference in your 180 yard point of impact is 2.3". I have called this "meaninglessly small", you be the judge for your own purposes.