How accurate are angle cosine indicators?

Jeff In TX

Well-Known Member
Aug 10, 2003
McKinney TX
How accurate are angle cosine indicators?

I remember one of my sniper courses covered this and we only used angle cosines for short ranging out around 300 yards max. If the shots were over 300 yards, the angle cosine weren’t very accurate as they only told you the angle distance, but it doesn’t take into account the time of flight of bullet and the additional drop the bullet experienced.

It’s been a long time since that training and living and shooting in Texas we don’t really have angle shots. Not many big hills here.

Anyone’s thoughts on the subject?

I'm going to get one and test it out this winter. I had the same question too.

We got some good hills her for testing it.
Made one from a Protractor and small bubble level. Attached it to the straight edge of the stock on the big 338/416 Rigby IMP.
It works fine.

Have four sets of drop charts I use that are also attached to the side of the stock. One at level shooting, one at 10 degrees another at 20 degrees and one at 30 degrees.
There is a difference in drops especially at every 10 degree increment from a level plane.

We find that, a spotter shot fired first will eleminate most any variance in drop or windage though as you can adjust to the impact and then swing back to the animal and kill it quickly. In most cases we don't use the incline indicator.

For those wanting to make a first shot hit at extreme range, you better know the wind patterns real good and this usually takes many years to "try" to figure out. Most never do figure it out.
The elevation indicator won't help a bit if a person don't know the wind "first".


[ 11-26-2003: Message edited by: Darryl Cassel ]
For those wanting to make a first shot hit at extreme range, you better know the wind patterns real good and this usually takes many years to "try" to figure out. Most never do figure it out.

It done successfully all the time, it just takes practice, some more than others.

Look at the aggs of the top scores at 1000 yards and you'll see who capable of keeping 'em all on POA for 10 shots, and who isn't.
They aren't all shot in perfect conditions either.

The elevation indicator won't help a bit if a person don't know the wind "first".

Actually I think you'd figure the static incline effect "first", then the wind speed and effect "immediately" preceeding the shot.

Knowing the angle effect is just as important as knowing how small of groups you're capable of printing on POA at what ever range you shoot, by what ever methed you use too. If it ain't smaller than kill zone size from POA, it ain't practical and is nothing more than a wish.

I don't think you have ever fired a 10 shot 1000 yard match so the procedure is probably new to you.

As for judging the wind at 1000 yard match, most fire their 5 or 10 shots (depending on what club your at) as fast as possible before the conditions change and move one or two of your bullet string to another part of the target.

That's why it's much easier to take a spotter shot first when hunting, and then swing right back on the animal with a final, fatal shot before the conditions have a chance to change like they would if you were firing 10 shots at a target. One shot as compared to 10 does make a difference.

When you shoot fast during aa match, the chances of having a better aggregate for the year is improved.

Anyway, the original post I made was, you better know the wind conditions real good and most never know how to do it correctly, even the 1000 yard match shooters. that's why most of them fire their rounds as fast as they possibly can. Usually 25 to 30 seconds for 10 shots in a 1000 yard benchrest match


[ 11-26-2003: Message edited by: Darryl Cassel ]

I tend to agree with Darryl here. Actually, He and I shot in a few relays together this year and several where his was a relay away from mine or that sort of thing. For the most part, we shot similar conditions, though sometimes one of us shot in horrible wind and the others relay was ok just later or vice versa. We shot on benches side by side and had extremely dissimmalar results and that's not uncommon there, especially at benches 1-5.

Just in the banquet shoot here in November, I shot the fourth relay. Relays 1 2 and 3 all shot 90's in absolutely dead calm conditions. Without a doubt, the best conditions of the year by a longshot. The fourth relay shot in what seemed to be excellent conditions also, but, all the scores dropped 10 points from bench 1 to 12. Here was a relay that over 1000 yards, I saw absolutely not one hint of condition and was blown farther off center than I had been all year (side to side). My score related to every other shooter in the relay and there were some excellent other shooters in the relays who shot great all year. Not a single one saw the change left in 4A and right in 4B. Not one. Now, all these shooters shoot at this range all the time and the flags showed absolutely nothing to any one of em.

We don't have flags over our game we hunt. And noone putting up spotters. Guessing the wind is something that people believe they can do only when they have shot thier entire life over easy conditions. Like, shooting where the wind is dead constant in 1 direction. If you show me a person who can read the wind at Cascade (Williamsport), well, I'd pay pretty good money to see that. The people who do well do just exactly what DC said AND they have guns that shoot well and they load well.

I know lots of people make great shots and I don't doubt that they can calculate a lot of the trajectory before pulling the trigger. But, all I can say is there is a lot more to reading conditions than what most people think. I know He'll tell ya that over the years a lot of people came to that range thinking they knew something about wind and could demonstrate that to the people there and left knowing they had a great deal yet to learn.

He's just saying that you have to be experienced with the terrain over which you shoot and even then sometimes you get stung. At the PA World open, we had a little wind and had hosts of people who couldn't keep 10 on. Shooters from our own club as well as from elsewhere. Even in the early morning relays, people had shots off.

I shoot at my house and I used to work out of my home. Every single day I would get my gun out for one and only one shot (at least) and shoot a steel target at some range (I have several) out my living room window off a bipod from the end table and couch. These would be anywhere from 300 yards 4" square to 600 yards 15" round. I prided myself on hits in ANY condition with a 22 cal every day. Make a good guess, dial, pow. Then I went to Cascade. Whooaaa!

I do not attempt to read wind any more. Period. My rule is, no adjustment over 8" under any circumstance. Period. That's all there is to it. There's just no guessin it here. Yes, people make an adjustment and guess right and win a relay and feel real proud of themselves. I've done that. But I'm not gonna try to BS you and tell you that I could do it again any other given day because anyone who knows the place would tell me correctly that I was full of excrement.

Now, to make a single shot on target at this kind of range... No deal. Perhaps elsewhere. Not here. I have yet to see a person show me otherwise. The terrain He hunts over where He lives is considerably steeper than this part of the state. I live on rolling hills, where 800ft is 2 miles from 1600ft of elevation. Wind is easy here. Pathetic. He's where 1500ft of change is 1/3mi. Wind has considerable verticle component AND it's swirling.

I know I'm gonna get a ton of argument on this, but, you know the saying, "I'm from Missouri, show me!" This isn't something anyone can come there to demonstrate. You'll just have to come here and try it out.

The real question is how accurate is a cosine indicator out past 300 yards.

As for reading wind, I'll agree with you. You better understand wind if you want to shoot long distances, say over 400 yards. The only way to get good at is to practice, practice and practice even more.

Shooting angles is the same thing. Just because you have the wind figured out, doesn't mean you have the angle worked out.

Shooting a 35 degree angle at 600 yards is roughly a 540 yard shot using a cosine angle. The time of flight of the bullet will actually be longer than flat 540 yards shot.

So would you trust a cosine indicator for a shot like this?? That's the real question?

Happy Turkey everyone.
Shooting a 35 degree angle at 600 yards is roughly a 540 yard shot using a cosine angle. The time of flight of the bullet will actually be longer than flat 540 yards shot.

So would you trust a cosine indicator for a shot like this?? That's the real question?

I guess I don't follow you on this one. If you range the target, the distance is the distance, regardless of the angle. Now, if you are ranging the first floor of a skyscraper from ground level and decide to shoot a pigeon at the 40th floor, now I see a change of range, but, If you have a Leica, you can range again to the bird and pow.

You also mentioned above (I don't have it in front of me) but something about the additional drop. There is no additional drop. If you are refering to the shot on an incline, that path will allways be high, though you will be hard pressed to build a gun capable of showing the difference from shot to shot. For that data you would have to provide some ballistics. Cal/Weight/BC/that sort of thing.

Now, unless I don't understand this cosine thing (I think I do) the 600 yd shot at 35 degrees relates to 491yards ground distance. I guess I have to do some reading on your gizmo you're talking about. It doesn't sound very fun to me. Shoot at stuff that doesn't run after the first round! Hehehe...
OK, I see the gizmo now. Well, I can't immagine using one effectively. It seems simple enough but I don't know where in the USA you get shots at such angles, (cept NYC shooting birds). Given the way it looks, I'd find a new toy and make 2 or 3 charts as DC said. Or, just shoot a spotter.

At 680 yds, 25 degrees = 11" Bullet path variation. Thats quite a steep hill to get a foot of change mister! Same thing as a 6-12 pitch roof for 680 yards.

I think I'd hunt somewhere else.

I really would like to know the answer to your question, it really buggin me too. The TOF thing I just can't work out, I do understand what you're saying though, completely. You might have just missed the thread in Equipment Reviews under cosine indicator, or something like that. TOF wasn't really discused, but it might be part of the answer to what was.

Maybe when Dave gets back from Wisconsin deer hunting he'll fix us up with an answer.

I'll call Jim Ristow and pick his brain about it tomarrow.

* * *

Phil, Darryl,

Seems you all are in a huricane up there at that range, must be fun!

I for one, couldn't fire 10 shots in 30 seconds even if I had a 10 round magazine, let alone breathe, aim and squeeze each one off with confidence... In 3 seconds wind can do alot of differnt stuff, let alone 30 seconds, even in the predominant condition.

If you guys are keeping decent groups in a rapid fire, your conditions hold for waaaaay longer than they ever do me, I'm lucky to have 3-5 seconds most of the time.

Are you guys suggesting reading wind is a waste of time, based on your shooting at the PA. range? Noone else has success reading wind anywhere else across the country, and they're just lucky if they repeat it and agg well with the method?

I simply don't shoot at certain ranges when I know I can't keep them all in the kill zone, that personal limit thing. And often I'm pretty limited too.

When I practice, they all stay on the target or I move closer, no point in wondering what's happing when you can know.

When we shoot in any wind, we know it can bite us if we under or over estimate, but by how much if we screw it up is the question I ask myself.

When I'm practicing, it's easy to see what range I'll need to be at to keep them all on the paper, which is usually almost twice as far away as I could keep them all in a kill zone.

I live and do most of my hunting in a 2 mile by 25 mile valley with mountains about 3-4 times as high as those, from the base, and we get wind too.

I'm kind of protected from the north wind out here 7 miles from Palmer, but I'll bet Michael is wondering if his roof is blown off about now, I heard it's blowin 50 mph in Palmer right now, not a breeze one over here though. We get the strong warm winds from the southeast through here is about all, and they get all the cold north winds.

I'm not sure "I've" got anything to really show anyone, but I would like to come see the usual 10 rounds in 30 seconds.

What seperates the winners from the loosers at the PA. range, you make it sound as though it's just dumb luck who wins?

It does sound like an AR-10T in 243 WIN or 300 WSM might be just the ticket over there.

[ 11-27-2003: Message edited by: Brent ]

In Colorado and up here in Cameron County, if you shoot from the bottom of the mountain to near the top or vice versa (depending on the length of the shot) you can get 20 and 30 degrees very often.

A 11" and larger drop can change the impact quite a lot if you are trying to get close to your spotter target on the first shot.


You can only use and load "ONE" shot at a time at Williamsport or at any IBS or NBRSA range. There are no multiple rounds allowed in a magazine. That makes the 30 second Benchrest shooting that much tougher when these guys fire fast.
When the front rests are set right and you have the rear rest adjusted right (heavy guns), the return to point of aim is right there most of the time. Almost like a return to battery system.
Some of our top shooters are VERY good at the speed shooting.

Sometimes they get caught but, not that often.

That's another reason most of us here promote a sighter shot "FIRST" when Long-range hunting.
It eleminates most of the variables and allows for the killer shot (which is in a matter of 3 to 5 seconds) next to be on target.

When some wanting to make 1st round hits, won't shoot because of high winds, we are able to do so using the sighter first, method

It works everytime and we have not had to make changes between the sighter and killing shots very often unless the wind does a complete reversal and we can see that quite easily even in the 3 to 5 second window.

To us, it's a team sport and the spotter is the important person on the team.

For those of you wondering about the spotter shot first---A sighter shot is taken 100 yards in front or behind the animal and on the same level as it is standing. This in no way spooks the animal as it never relates that sound of impact to anything because it does not hear the muzzle blast at the far distance we are shooting. We are then able to make the scope corrections quickly and swing onto it for the killing shot.

Sometimes two spotters are needed first. These spotters can be made at a open patch of dirt, a dead stump base or even a small rock.
In steep mountain terrain, it works everytime.

Later and Happy Thanksgiving to all.
We are having PA wild turkey today. Makes the meal that much nicer.


[ 11-27-2003: Message edited by: Darryl Cassel ]

You don't have to read into the incline shooting as to what you may have.

You mentioned that a shot at 600 would be 540 at an angle.

What I want from my incline indicator is, how many MOA "difference" is there to the animal at the "ACTUAL" range he is at?

If an animal is ranged at 1000 yards and at 30 degrees (up or down), I want to know what the difference is I will need in MOA if he was standing on the level or zero degrees from my rifle at 1000 yards. Hence, two drop charts. You must use the rangfinder and get his range no matter what degree he is standing in the mountain or valley. "Actual" yardage from the rifle barrel to that animal is the key here.

For instance, if you run your ballistics chart at zero degrees and 1000 yards and make a drop chart, then program in 30 degrees with no other changes other then degrees, and make another drop chart then you can see the difference of MOA change you will need to make the 30 degree shot if the animal is at the same distance in any degree.

Many longrange guns will have a more or less (depending on the angle up or down) at 30 degrees of 2 MOA change from the same distance on the level.
1 MOA at 1000 yards is roughly 10" so a 20" change was made going from 1000 yards on flat land to a 30 degree shot at 1000 yards also.

Run the numbers on your program and you will know what the difference is but, make sure the range is on flat ground or at a 10, 20, or 30 degree shot and is the "SAME" in distance. The rangefinder is the important factor here to.


[ 11-27-2003: Message edited by: Darryl Cassel ]
Your are correct a 600 yard shot at a 35 degree angle is around 490 yards.

The point I was trying to make is the bullet will actually travel 600 yards to the target, but because of the anfle it is actually a 490 yard shot. Time of flight is almost 20 percent longer. Using a cosine only tells you the shot is 490 yards. Atleast that's how we were taught in our tactical training.

According to my RSI ballistic Lab. There is around 3 MOA (roughly 15 inches) difference between using a cosine verses calculating the angle of fire and figuring in the actual time of flight for the bullet.

I hope that makes better sense.

Anyhow, I'm off to stuff my self full of Turkey and fixen's.

God Bless everyone and I hope everyone enjoys their Thanksgiving!
Hello again

We are saying the same thing only adding a twist to it.

When I range an animal for "actual" yardage--- A 600 yard shot at a 30 degree angle is 600 yards. When I range an animal at 600 yards on the level its 600 yards.

If you range "any" animal at a certain distance, that's how far away he is from the rifle regardless if he's on an incline or on the level ground.
It doesn't matter if he's at 35 degrees up or down or on the level. If the rangefinder says it is 1000 yards at 35 degreeas and he moves down to the level ground you are on and the rangefinder is used again on him and it still says 1000 yards, that's his distance from you.

We don't have to triangulate his position and say that if he was on the level at this distance, then that would mean that his position would be something else or a different yardage at 30 degrees. You really don't have to figure another step such as Time of Flight because a distance may be different "IF" that animal was at another position to start with.

The only thing I want to know when I shoot at an animal that is at 20 or 30 degrees up or down from my shooting spot is-----what is the MOA difference between the zero level shot and the angle shot at the "SAME" distance in yards or meters.

Maybe that's a bit clearer?

Anyway, good shooting to you and hope you don't stuff yourself to bad that you get sick.


[ 11-27-2003: Message edited by: Darryl Cassel ]
Warning! This thread is more than 20 years ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.