Do you use an Angle Cosine Indicator (ACI) for uphill/downhill shots?

[Pons]

I copied this from a write up on another site. Still trying to figure what he's saying. Wish the author would've include a sample diagram. Anyone use this method? If so, how about more detail.

"Another Rule-of-Thumb, suggested to me by Sergeant Neal Terry, a longtime
sniper instructor and police SWAT sniper, is to draw an invisible vertical line
through the up or down target, and where this line intersects the earth's surface,
range it! Disregard the angle, ignore the direct distance from muzzle-to-target,
concentrate only on adjusting elevation for the distance to where that vertical line
touches the earth. Compensate for that distance, aim dead-on and fire. We've
worn out several pads of paper comparing Neal's math to other kinds of up/down
calculations - it works and it's the essence of simplicity!"

That method takes the horizontal component of the distance and using that for range ("rifleman" method). It could be useful in some scenarios. You could do the same thing with the Angle/Cosine indicator if you multiplied the cos of the angle against the distance ranged to target.

Some nice things about the a/c indicator, you don't need a very steep background that is nearly the same horizontal distance from you as the horizontal component of the distance of your target to you. You could multiply the cos of the angle by your moa adjustment for the direct range (see link to article below) to get a hold estimation. Finally, you could enter the angle into a good ballistics program and get a more precise model of what adjustment is needed to get on target. see - http://www.longrangehunting.com/articles/angle-shooting.php

You could run some simulations using angles and the three different methods, then see what you get. Is your method getting you "close enough" to be "on target"? After all, isn't that the goal of much of this?

Hope that helps Triple BB


Here is an article with some diagrams and better explanation. http://www.longrangehunting.com/articles/angle-shooting.php

 

[Silverback7]

They are so easy to use and once you get used to the math you can estimate pretty darn quick

 

[1Hunter]

I bought a small inclinometer in the early 80's from a survey equipment shop.
I used it alot shooting Field tournaments and I always managed to pick up
a few points from my competitors who merely guessed how much to cut
yardage on the down hill targets. Still do as a matter of fact when I go Bow
Hunting. The new range finders with the angle built in are great.

1Hunter

 

[985]

1Hunter,

Here's the skinny on most Civilian LRF's EXCEPT for the Swarovsky.
The LRF's have the electronics or diode attached to a plastic "stick" called a gate. This plastic gate is able to be adjusted by a screw so that the diode sits centered, directly behind the lens. If you hunt in freezing temperatures, and do not keep the LRF heated, the plastic gate will react to the cold temperature and twist / warp. That will be the end of the LRF.

SWAROVSKY IS THE ONLY CIVILIAN LRF THAT I OWN. IT IS DEPENDABLE, AND THE COMPANY IS TRULY REPUTABLE. THE LRF THAT I OWN WORKS OUT TO 1837 METERS. IN MID DAY SUNLIGHT IT RANGES RELIABLY AT OR BEYOND 1500 METERS.

 

[1Hunter]

I realy like Swarovsky, especially their lens. The only thing is I
have to take a deep breath when I buy one. Usually costs a
piece of the farm. But, usually worth it.

1Hunter

 

[985]

I think that the Swarovsky LRF is under $900.00.
IF you want one that will last you years instead of months, it's really the way to go.

 

[joe0121]

CALL ME CHEAP! I use a 10 dollar angle finder from ace hardware.
RR

You can also use a mil-dot master.

 

[McMillan]

I shot a black bear at 535 yards on a 37 degree down inclination using a NightForce Velocity reticle. Can anyone guess what yardage line I needed to hold on to make a perfect shot? BTW, I did make a perfect shot with a McMillan EOL Outdoorsman in 300 EOL mag. the a 5.5-22x56 NF scope with the above mentioned reticle, level and ACI installed on the ring cap. This is a standard set up for our EOL packages.

 

[paphil]

I'd a dialed about 425 yards and let it fly. cosine for that angle is about -20 yds per 100.

 

[985]

Right on. Sniper Tools Design Co ACI Durability Test - YouTube

 

[1Hunter]

I shot a black bear at 535 yards on a 37 degree down inclination using a NightForce Velocity reticle. Can anyone guess what yardage line I needed to hold on to make a perfect shot? BTW, I did make a perfect shot with a McMillan EOL Outdoorsman in 300 EOL mag. the a 5.5-22x56 NF scope with the above mentioned reticle, level and ACI installed on the ring cap. This is a standard set up for our EOL packages.

Since my equipment is much older than your using. I have to rely on visual sightings to acheive angle degree, it is necessary for me to consult a known
trajectory scale for a given weight. also The wind factor if any, the the time of
day for possible correction for mirage if any. I'd pray for a perfect miss rather
than a hit that wasn't perfect.

Good Luck and keep them in the middle.

 

[McMillan]

I actually held right on 500. It was suggested 20 yards per 100 but that may be uphill rather than downhill.

 

[paphil]

Uphill and downhill are both the same. You will subtract yardage for both. You were very lucky to have hit the bear at all.

 

[McMillan]

I guess the reason I was able to hit the bear was that I made exactly the compensation the NightForce ballistic program told me to make, and it must have been right because the bullet went exactly where it was supposed to. The only thing I might possibly be wrong about is the angle of declination. Not sure I remember that exactly. What I do remember is that it was a real bear, no pun intended, getting back up the mountain. If you look at the angle of the spotting scope that will give you a true reading of the angle.