How accurate are angle cosine indicators?

Brent

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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...


We might be able to just as well but, we are just willing to admit that conditions do change between shots, 3-5-10-15-30 seconds, it makes no difference, they do change and you must be able to read wind to see it, even after a sighter shot. Unless you can read the wind, and take steps to do so, there's no way you'd detect a change in the first place. Even if you can, there's no guarantee you'll get it right every time, but you WILL greatly increase your chances. Burying your head in the sand and ignoring facts is no excuse when you're shooting at big game at near 1000 yards, much less 2000 yards or more. I've yet to see a single picture of an animal killed at extreme long range showing the shot placement in its kill zone, much less pix of numerous such kills. You'd think someone would have had a camera at least a few times in 20 some years...
I am not doubting that kills have been made, just that the claimed precision is smoke and mirrors.

Phils quote seems to fit well here, so I'll use it:

I know I'm gonna get a ton of argument on this, but, you know the saying, "I'm from Missouri, show me!"


* * *


Jeff,

I don't think DC has compared the results from using the cosine method vs. the angle method his program predicts? I think he'd of seen the difference in the predicted MOA required if he had, because they aren't near the same thing.


Both are said to be right, but both do not agree. This is the issue here. WHY one IS right, and the other is NOT is what Jeff is looking to be explained etc, both cannot be right is the point.

Hopefully this can be explored more fully until it makes sense. I don't really understand what DC was really trying to communicate, kind of left me confused. Sorry DC, in the end, you may be right though and the angle calculation in the ballistic programs might be the correct one to use. But still, why?
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Jeff In TX

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OK dinners done and I'm stuff, but I'll try this again.

In the first example it was a 600 shot with a 35 degree angle. The cosine distance shows the shot to be a 490 yard shot.
Using my 308 zeroed at 100 yard and 2700'
A 490 yard shot with my .308 would have -53.13 inch path (drop).
A 600 yard shot using a calculated trajectory would have a -71.01 inch path. This gives us a difference of almost 18 inches. The calculated trajectory is taking into consideration the additional bullet flight time which still has gravity pulling on it.

Not many shots would fall under this catagory, but it goes to show you just can't use a cosine angle for long range shots. Shot under 300 yards with a 20 angle there isn't much difference, but go over 300 yards and increase the angle and it's a whole new ball game.

Now I hope that made since.
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[ 11-27-2003: Message edited by: Jeff In TX ]
 

Darryl Cassel

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Brent

It's Because the angle adjustment is "direct" to the target in yards or meters.

The same with a direct shot at an animal on level ground.

The target is aquired "after" it has been ranged no matter if it is on a level surface plane or an angle.

The distance to the animal is "direct."

Let the program do the math.

If a target is aquired through ranging at 1000 yards on level ground and is 1000 yards away, a rifle (could be several calibers) would need 22 MOA to make the hit.
At 30 degree incline and at 1000 yards, that same rifle would need 20MOA to make the hit.

It's simply a 2 MOA change to your elevation clicks no matter if it's at 30 degrees or on level as long as the animal, is in fact, 1000 yards a way.

If a person is not using a Rangefinder to acquire the target then they really don't know the "actual" distance to that animal now do they?

On another note--- If you were referring to me in your statement.
It doesn't matter to me if you believe the shots or not that we made in the past. We had witnesses on the long kills and the pics I took back then were on slides and printed pics. The 35MM cameras I own are much lighter then my Sony Mavica camera. needless to say, when we go after game across the Colorado mountains, you go as light as possible since you already have a large freighter back pack on to bring the meat back. I really wasn't concerned about showing pics of bullet placement at the time. The animal was very dead and our concern was to get it out. No digital cameras were with us back then even on shorter shots of 1200 to 1350 yards.. My scanner is broken and I have not replaced it so I can't send you any proof. Frankly I don't need to. Anyone who knows me, knows that I don't tell stories about hunting trips or anything for that matter.
I've been a Longrange hunter to long to do anything like that.
Trust me, the kills were made and you don't have to believe it at all, OK?

Later
DC
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PS---I didn't take a pic of the wild turkey I shot and we had today either. Should I have done that to prove I killed that too, Brent?

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

4mesh063

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Jeff,

I see now how there could be a change on the time of flight thing that may also vary the numbers you would get if calculating with a Cosine indicator, but, I am guessing that since the device is giving a variation from level to 30 deg of 11" as I said before at that predetermined range, the total error in that calculation being a such a small percentage will probably be far less than the error in accuracy of the gun and thus becomes a non issue. As Harold Vaughn Says, 5 6" errors produce a 14" group. (sum of squares). If I was to use this for a hunting tool, I would probably opt for the several chart method as DC says. It never enters into my hunting as the angles are not as great as to cause a problem worth worring about. (to me). My mountain is 7 degrees of total rise. There are steeper parts in it, but over the distance I shoot, it's only 7 degrees of angle. And it's a bitch to walk up. That's why I say I find it hard to believe that people shoot at game 25 degrees up and then go get it. I'd need a heilicopter to get there. Better yet, I wouldn't shoot.

Speaking of which, Brent. Keep in mind that the practice we get in wind reading at the 1000yd range is done when out relay is up. We don't worry about wounding the targets. (I have). I won't speak for DC, but, I'll wager he'll agree. We shot 4 or so matches this year where I wouldn't have considered shooting at game. In addition, by the time hunting season comes here, at least if it's good and cold, the wind situation is way less than it is in the shooting season. Third, I am looking at my deer at 6:35 in the morning, not 11:00 in the morning. Our earliest relay is 9:00 IF the match is underway. 9:20 Relay 2, etc. If we are delayed as we were several times this season, it may be worse. Several mornings relay 1 was at 10:30 because of fog. We waited till the wind started, then shot. There's not much fog in hunting season here. So, the shooting situations are very different. More than once this year, I had a hard time getting on a 62x42 target, with help. Much less shooting at game when the darn things won't spot my shots for me!

More variations from hunting to match shooting. Anyone who has shot sighter periods will tell you that movements, unless in horrible conditions can be watched and tracked and the shots will migrate around the target. Sighters are easy to shoot. They mark the shot and you dial right into the center of the target. It's the cease fire, then the 1 minute delay then the commence fire and the time it takes to get 10 rounds off that's the trouble. When I'm shooting at a deer, my spotter doesn't call 2 minute cease fires just to screw me up. There is a HUGE difference between getting a gun to have 2 or 3 shots follow each other, and getting a gun to shoot 10 sighters, heat up, wait a minute and then group 10 more shots out of and already hot barrel AND score under conditions you would never hunt in. I have seen people make claims to being able to "read" wind in such a way to calculate shot placement at the same ranges I hunt, but do it in conditions that I wouldn't hunt. I seem to remember a person saying that in a 25mph wind at a distance of 1100 yards or something like that, that they made a 1 shot kill. Enter the Missouri quote again! Sad part is, I believe that there may not have been any exaggeration, but I'd still like to see it. I for one won't make that shot until I'm satisfied and confident. That'll be a while.

As for DC saying "high winds", I'd be surprised if the shots he's made in significant wind, were made at past 1K. Up t 1K, I'd virtually bet my life that I could shoot a good shot from 2 spotter shots. Provided I could see them or the spotter could. My aggs this year with my light gun were both 12" and the gun was broke the entire year. So, I was still able to put 10 shots in a foot at 1023 under all sorts of conditions and that was the average group for 10 shots. I shot WAY worse than I did the year before and only shot part of that season. Well, one of those 10 shots ought to be able to kill something. Even after the cease fires, I'd bet that 70% of my plot sheets show shot # 1 in the 10 ring. Well, that's the one that goes after the game and in the 10 ring means that it's within 3" of the point of aim. Match shooting may be a year round warmup for hunting season, but the 2 games are entirely different and in a way, hunting is easier. In some other ways, it's harder.

The long and short of it, We shoot 10 shots for record in a match. BUT, we get scored for shots 11-20, not shots 1-10. There's a big difference.
 

dwm

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Gravity only applies during the time of flight that the bullet is traveling in the horizontal distance to the target.

The distance to the target measured by a laser range finder = the hypotenuse of a triangle.

The horizontal distance to the target = laser measured distance * cosine of the angle

Example:

Target at 30 degrees up and 600 yards away as measured by laser range finder

Horizontal distance = 600 yards * cosine(30) = ~520 yards

So instead of calculating bullet drop/clicks for 600 yards you calculate bullet drop/clicks for 520 yards.


Cosine table:
Angle: Cosine of angle: Cosine(angle) * 600 yards
0 1 600 yards
5 0.9962 597 yards
10 0.9848 590 yards
15 0.9659 580 yards
20 0.9397 563 yards
25 0.9063 543 yards
30 0.8660 520 yards

Something to note here is that the cosine of small angles (0 to 5 degrees) is very close to 1 and can be ignored.

So either do the math or take a spotter shot.

Hope this helps.


One more thing - if you have a MIL-DOT reticule, the MIL-DOT Master provides a quick way to calculate all of these issues including effects of the wind:

About the Mildot Master® (http://www.mildot.com/)

The Mildot Master® is an analog calculator designed along the principle of a slide rule, utilizing logarithmic and inverse logarithmic scales developed specifically for performing the following operations:

- Rapid and simple calculation of range to target, based on a measurement of the target with a mildot reticule, by aligning the estimated target size directly opposite the mildot measurement, and then reading the range at an index mark.

- Rapid and simple calculation of the amount of sight correction necessary to compensate for bullet drop and/or wind drift for a given range, enabling the shooter to determine either the equivalent telescopic sight adjustment (minute-of-angle, or MOA) or the equivalent hold-over (mils), by reading equivalents in both MOA and mils directly opposite the bullet drop/wind drift figure.

- Additionally, angle of fire for uphill or downhill shots can be accurately measured, and the up/down compensation can be closely calculated to reduce the errors such shots can induce.

Doug

[ 11-28-2003: Message edited by: dwm ]

[ 11-28-2003: Message edited by: dwm ]
 

Darryl Cassel

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Thanks Doug for the info.

As you stated, do the math or take the sighter shot first.

I have always taken the sighter shot first.

The two drop charts work also but, the spotter shot method is much faster and seems more accurate to "me", since you can see the impacts and adjust to it.
If I didn't use the spotter method and click to impact, I would go to the Mill dot and have the mildot master on hand.
I just don't like a lot of lines or dots in my field of view when looking through a scope.

Thanks again.
DC
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[ 11-28-2003: Message edited by: Darryl Cassel ]
 

Jeff In TX

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DMW,

I'm going to have to disagree here.

"Gravity only applies during the time of flight that the bullet is traveling in the horizontal distance to the target."

The horizontal distance to the target = laser measured distance * cosine of the angle

Example:

Target at 30 degrees up and 600 yards away as measured by laser range finder

Horizontal distance = 600 yards * cosine(30) = ~520 yards

So instead of calculating bullet drop/clicks for 600 yards you calculate bullet drop/clicks for 520 yards.

That statement is 100% Incorrect! Simple physics tells us that’s an incorrect statement. The only time gravity really doesn't come into play is if the shot is strait down at 90 degrees.

I’ve been through too much tactical and long distance shooting training not to mention college courses on physics to believe a statement like that.

One must first have to understand ballistics (not saying you don’t), most really don’t. I’ve really gotten into the ballistic calculations for the last three years trying to understand it all. Bottom line, I’ve still got a lot learn. When I see or hear people using a ballistic calculator and using a G1 drag coefficient when shooting a boat tail bullets or VLD’s and not a 1” 1 pound round nose projectile it only goes to show how much they really don’t understand what they are doing.

Like I said, a cosine angle will work fine out 300 yards and not very sharp angles. After that, you need to understand the bigger picture.

Ahh, disagreements & constructive criticism, only helps to further discussions and sooner or later we eventually get to the correct answer.

[ 11-28-2003: Message edited by: Jeff In TX ]
 

Darryl Cassel

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jeff

That's the way I see it to.

That's another reason I rely on the MOA difference of 600 yards as apposed to 520 yards and see what the MOA change is within the Oehler Program at 30 or 35 degrees.

Has worked for us but, like I said earlier, I take a spotter shot to make sure.

later
DC
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dwm

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I'd rather not argue about the gravity thing, it is a fact. Gravity only applies to the horizontal component of the bullets trajectory.

Basic laws of physics and vector mechanics apply. (Trust the nerdy engineer on this one.)

It's a gravity thing.

I could look up some references for you if you want to read about it.

Doug
 

Darryl Cassel

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Doug

Isn't it a fact that the gravitational pull is simply less on angle shooting rather then just straight out Horizontal or level shooting?

The bullet is still "mostly" horizontal on a 30 or 35 degree incline shot? It's just slightly elevated. It would have to have pull from gravitaion, just slightly less?

I thought I had read about this years ago and it even gave the lower percentage of pull at different angles and along the bullets path.

Later
DC
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dwm

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My example above provides the basic theory but it did leave one thing out:

It did not take into consideration that the scope and the barrel are not aligned in parallel. The scope to barrel angle has to be added in also. We all have zeroed our rifles to compensate for a particular trajectory and this needs to be factored into the calculation.

Darryl, look in the Sierra Reloading Manual. There is a section on up/down hill shooting. It does not present the math behind it all, but does have tables to compensate for various angles.

I don't have the manual, just the software version.

Don Lilja has a paragraph or two in the long range shooting section of his web site.

There are a lot of interesting things to read on the web if you do a web search on "shooting uphill".

[ 11-28-2003: Message edited by: dwm ]
 

Jeff In TX

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OK here’s the scenario.

Urban tactical situation. Roof top tactical shooter, bad guy is laser ranged at 120 yards. Angle of the shot is 60 degrees.

Shooting a 168 sierra BTHP at 2600” per second. You get one shot to drop the bad guy. Officer in-charge at the seen gives you the green light. Lives are on the line and you only get one shot. Do you use the cosine angle, which makes it a 60-yard shot, or do you use a calculated ballistic drop for 120 yards?

Sorry folks, no spotter shot for this one.
 

Darryl Cassel

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Jeff

I would have drop charts for the rifle I was using and have 0, 10, 20, 30, 40, 50 and 60 degree charts for the angles I may encounter.

These charts would also have the various ranges out to 500 yards in 25 yard increments if this was a city situation.

Small drop charts can be carried on the person or taped to the stock of the rifle.

Later
DC

[ 11-28-2003: Message edited by: Darryl Cassel ]
 
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