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How accurate are angle cosine indicators?

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Unread 11-28-2003, 06:50 PM
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Join Date: Aug 2003
Location: McKinney TX
Posts: 408
Re: How accurate are angle cosine indicators?


[img]images/icons/smile.gif[/img] I fully understand about log books and data sheets. 99% of the shot I've taken over the last 10+ years are in my log books. I have a chart for just about everything and there not done from a computer, but from actual shots in the field and on the range.

I was simply trying to stress a point. Using cosine angles are only so accurate. If you understand how it really works, you can make a first shot hit without a spotter shot, atleast out to 400 yards.

Anyway, thanks for all the input. This is what makes this board so good.

Mathew 5:16

Distance is not an issue, but the wind will make it interesting!
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Unread 11-28-2003, 07:36 PM
dwm dwm is offline
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Join Date: Feb 2003
Location: Texas
Posts: 725
Re: How accurate are angle cosine indicators?

The way I see it in today's high tech game, you have three choices:

1. Laser range finder plus handheld computer with actual drop charts and ballistic program installed.

Does the military issue hand helds to the present day long range marksmen?

2. Laser range finder with drop charts

3. MIL-DOT scope plus MIL-DOT Master

There is still the outstanding issue of estimating the angle though. At long range and/or steep angles, the accuracy of estimating the angle and the amount of angle involved make a big difference in where the bullet hits.

I think all techniques will work as long as the marksman understands his chosen approach and trains accordingly.

[ 11-28-2003: Message edited by: dwm ]
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Unread 11-28-2003, 11:25 PM
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Re: How accurate are angle cosine indicators?;t=000146;p=2
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Unread 11-29-2003, 12:12 AM
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Location: Palmer, Alaska
Posts: 2,539
Re: How accurate are angle cosine indicators?


The formula that the angle function in the ballistic programs use is as follows:

Path in inches = P - (1.0 - C * D)

P = Path of bullet at level fire in inches.
C = Cosine of angle.
D = Total bullet drop at range in inches.

Increase in bullet path height:

5 deg .004
10 .015
15 .034
20 .060
25 .094
30 .134
35 .181
40 .234
45 .293
50 .357
55 .426
60 .500

Multiply the total bullet drop at the actual range by the number above fo a given angle, subtract this amount in inches from the bullet path at level fire. This will now be the new bullet path for that angle.

This is how they calculate it, I'm still not sure why the multiple they use happens to be 1.0 minus the cosine of the angle.

* * *

The kills are not in question, like I said. What happens to be, is the precision and repeatabilty of the sighter shot(s) and kill shot.

For one to put 3 rounds on POA at 2000 yards for instance, 2 sighters and 1 kill shot, what does it take to do this?

Lets take a look.
For round numbers sake, I'll use a 20" x 20" kill zone to illistrate this, close to an Elk anyway.
A rifle capable of shooting sub 1 MOA 3 shot groups should do it right? Hypothetically, yes, in the real world, no. It's not going to be anywhere linier at 2000 yards. Even 1000 yard shooters will tell you it isn't linier there either.
How small will your rifle print three shots at 2000 yards?

Variables associated with each of the shots, reguardless of if a sighter or two is taken:

Muzzle velocity ES.
Ballistic coefficient ES.

Variables associated with the sighter shot(s) themselves, reguarding rezeroing the rifle at the target distance:

No Russian laser rangefinder, Lieca Vector, B&S or Wild, and you're probably screwed from the start.

Spotter does not have a measurement method to determine how far POI is from POA, or an exact way to convey POI location to shooter if shooter does not see the hit.

This is if the spotter can even identify the POI in the first place. 2000 yards with 20x eye pieces is, well, a long friggin ways still.

POI to POA adjustment after a sighter fired requires shooter to again line up on original POA and dial reticle to POI location to zero on sighter, or possible to a location in between two or more sighters fired.

This brings up a problem with zeroing off of a single sighter, or possibly two, and them calling the rifle perfectly zeroed. Sorry, it ain't so. You very well could be zeroing off of a shot that's POI was unusually low, high, left or right. The next shot, or two may very well be in a completely different location within the group... thus the rifle is not zeroed at all, just close. But how close?

Well let's see... If you zero the rifle on a shot that was at an exteme low (low shot in the MV ES maybe), you're now are suceptible to missing the animal completely if you have another shot that shoots low in a group for some reason. The more shots you fire to sight in on, the less possibility of this happening. Still very likely with only two sighters to zero by tho, just one makes it even more likely. If this weren't the case, at 1000 yard BR, they'd never make use of 10 sighters, now would they.

Now, while you're doing all this fiddling around taking sighter shots and dialing the reticle in to POI, the wind does have time to change, very easily plenty of time too.
At 1000 yard BR, these guys have the benifit of a target with calibrated rings, so when a bullet hits, they know how many MOA off it is with a quick look back at it, not so with the stump, bare patch of ground or what ever the sighter is fired into in the field. It has to be guaged some how before the sight adjustment takes place, this takes a few seconds to determine and adjust, at least a few seconds.

Then if you're smart, you look to see if the wind has changed in any way out to the target, more time. You fire a second sighter to verify, possibly, and if you're quick you get on to see how far it was off, still no way to measure it, but a good guess works. Now you either adjust again, and or swing to the animal, one last look for a wind change, and fire the kill shot if not...

The sighter shots do help in some ways, but the method has serious downfalls as pointed out. It's not without problems, by any stretch of the imagination. [img]images/icons/wink.gif[/img]

The explanation often given for how the method is employed is really quite a limited one and very misleading to anyone that's not thought the whole thing through with some knowledge of ballistics at LR.

I once thought it seemed to be a great method, but the more I learned about ballistics and what really happens at 1000 yards and beyond, the flaws in it really couldn't be ignored, as they seems to be by others. But then again, I know more than half the guys on this site are savy enough to understand what I've just outlined.

With only one or two sighter shots, I'm not confident it works as accurately as it's cracked up to, much less at 2000 yards. The facts just speak to clearly. [img]images/icons/wink.gif[/img]

Enjoy your hunting method tho, I do mine. [img]images/icons/smile.gif[/img]

[ 11-29-2003: Message edited by: Brent ]
Brent Moffitt
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Unread 11-29-2003, 01:24 AM
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Re: How accurate are angle cosine indicators?

Thanks for the link Dimitrios. [img]images/icons/smile.gif[/img]

I read the second page there and it was enlightening. Wouldn't display the first page but, I think what Mike is saying is the total drop from the muzzle * the cosine of the angle is the true answer, either in MOA or inches. I've not checked it out yet, but I'll bet that's the correct method, most accurate anyway. The other method, drop * cosine from the 100 yard zero is real close, and might be easier with those numbers in memmory vs the total drop numbers. Definitely a step up in accuracy over the range * cosine method, which sounds like it's really the one that isn't accurate out far, or with steep slopes.

Thanks again for the link. [img]images/icons/smile.gif[/img] I'll have to see if the fist page comes up tomarrow, I'd like to read it too.
Brent Moffitt
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Unread 11-29-2003, 08:44 AM
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Location: Pennsylvania
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Re: How accurate are angle cosine indicators?


As you said, on paper and the real world, are two different things.

I have found that the spotter method is truly the most accurate way to place a shot from point A to point B at extreme range over 1000 yards.

That's why there is a spotter period in 1000 yard benchrest shooting. Someone trying to shoot their 10 match rounds without sighters at a 1000 yard target is just fooling themselves.

So why not employ the spotter method rational to 1000 yard plus shooting?

It has worked for us out to 2100 yards and to a friend of mine out to 2890 Yards on elk.

Of course "all" first round hits after the sighter round shot/s, are not "strickly" in the kill zone "every" time. Just like your method would certainly not be.

This does not matter as the distance we are shooting, the animal is not alarmed from the muzzle blast and just lays down when hit even when it's not in a fatal area.

I saw a friend of mine hit a large bull elk with his 30/378 long barreled rifle at 1350 yards. His shot hit right in the middle of the rib cage. It was behind the heart and lung area. The whole side of the elk just shook drasticly and he took two steps "backwards" and layed down on the spot. The next round, within 5 seconds after he laid down took it in the neck and it was dead.

I saw another one one time that another friend shot and the first hit was low in the shoulder. Not a killing hit. The elk laid down and the next shot was placed in the head to end any misery he may have had in those last few seconds of his life.

There are downfalls to every type of Longrange hunting and every shot is different.

The fact remains that the spotter shot first method is the only "true" and exact way of judging the wind and adjusting the scope elevation and windage for the killing shot.

At 1000 yards and under, it is quite easy to make 1st round hits/kills but past that, the game changes.
I killed a buck up here in Norhtern PA that was out at 1000 yards. No sighter shot was taken and the bullet hit at the base of the neck and it was dead right there.

Killed two Mule deer back to back (My buddy one and I got the other)at 1050 yards in Colorado. One shot for each deer and no spotters needed at all.

Like I said over that yardage (1000 yards), a spotter is needed and when a swich is seen in the wind, another spotter is taken.

It has worked for us for many years but the fact remains, "most" of the shots are in the kill zone and normally through at least one shoulder. We have not lost an animal to date that was hit by our Long-rage rifles and thats a lot of years of hunting and alot of game taken.

I wish I were in Alaska and had the chance to use the spotter method there as it looks like the area we hunt in Colorado.

"All" extreme Longrange hunters from PA who travel west to hunt and here in the North Central part of the State use the spotter method and it works well for all of us.

Like I mentioned before, there are "many" LR hunters that come to this area and I have a chance to travel around and talk to most of them in the two weeks of Buck season after I have taken mine. Most times I get invited to sit and glass with them and help spot which I like to do.

They all use the spotter method as they want to be as close as possible to the kill zone when they take their shot at the animal. No other method I have found will allow this.

Anyway, what works for us is one thing and what works for you is another.
I'll keep the spotter method as I have not seen a better way yet and have tried most every way there is over the years.

I've tried the multiple dots in the scope, the ranging style scopes and don't like them at all. I don't like to see a lot of lines and dots in the view.
I personnaly like the fine cross hair or 1/4 MIN dot to look through in my scopes. I have a NF-NXS with the 2-DD that works well though. I think the CH 1,2 or 3 would be even better for our style of LR hunting.

I guess you can say, it's what ever trips your trigger that counts and to each his own. Whatever works for "you" or "me" or anyone else is the important thing.

Later and Good hunting.
DC [img]images/icons/smile.gif[/img]

On another note----Does your Oehler 43 have it's own printout and screen like the 35-P or do you have to use a laptop computer and printer with it in the field?
Most 43s I've seen, you have to have a computer?

[ 11-29-2003: Message edited by: Darryl Cassel ]
Darryl Cassel
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Unread 11-29-2003, 03:16 PM
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Location: Palmer, Alaska
Posts: 2,539
Re: How accurate are angle cosine indicators?


I appreciate that whole picture explaination of your success with it, makes sense. [img]images/icons/smile.gif[/img]

I'll keep my range limited to what I feel sure of, and that's still under 1000 yards by a ways. Keeping POI within 8" of POA every shot is still my personal range limitation test. This gives me a little wiggle room on a moose, with the wind being by far the worst variable, range determination will definitely come into the picture as the range increases.

The M43 relies on a laptop to work, so does PressureTrace. The tests are saved and then printed at home on the printer here, although you could bring a printer along with you too. It's too easy to replay the test on the computer if I need to see it at the range tho.

The computer and strain gage leads are hooked to the M43, sky screens too if you're measuring MV or down range velocity, which I usually do as well. The computer is plugged into the DC charger and into the cigar lighter socket in the truck, or into the battery booster pack I bring along.

If we're in the field testing and not at the local range, the computer sets on the truck seat next to the bench, with the on the bench.

I use a PDA with Exbal for my drops when shooting LR. The Kestrel graphs the wind speed at the muzzle in 2 second intervals. The predominant condition and its duration is identified and then used as a referance.

* * *

After doing a little checking, I found if you multiply the total bullet drop from the muzzle by the cosine of the angle, which the ACI will give you, you will indeed end up with the exact solution predicted by the programs with that angle entered in.

Take the example given in the Sierra handgun manual for instance:

44 Mag
240gr JHC
1400 fps
.186 BC
Standard conditions at 5000 ft:
Temp = 41.2
BP = 24.52
Hum = 78
Adjusted BC = .2159

Sight height = 1.2
Impact range = 500 yards
Incline angle = 60 degrees (cosine .500)

Drop = 375.56" or 71.72 MOA = (375.56 * 1.047 / 5)
Path = 35.86 MOA = (71.72 * cosine of .500)

Path on program = 35.86 MOA also, so this is indeed the formula they use. At least that's explained now. [img]images/icons/smile.gif[/img]
Brent Moffitt
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