A protractor with plumb bob hanging from it does work, but kinda hard to point it exactly at your target and still read the numbers on the side.

IMO, the rifle mounted system with angle or cosine indicator is the way to go. When mounting it, we can ensure the rifle is plumb level and that the indicator reads 0 at the same time.

Some rangefinders now give the shot angle too, which is a great idea I think.

Least accurate method is to use the cosine times the "line of sight" distance, as Michaels post illustrates.

I have the ACI, which is cosine tool,OR angle tool,They do the same thing. It just depends how you input your math.I dont have PDA YET, so cosine is easier for me. IT reads on dial0,99,98,96,94,91 etc for cosine,BUt these are also all 5 degree increments down the dial, you just have to keep that in mind,I marked mine w/dremel on one side so I HAVE BOTH.

Not trying to start an argument here, but I have a real life experience that happened about 15 years ago, that made me realize the standard "shoot to distance" or normal cosine type of calculation is not as precise as needed sometimes.

Shooting rockchucks high up on a cliff. Laying flat on my back on basically level ground. Had my rifle proped up on 36" tall shooting sticks that were only about a foot and 1/2 from my armpit..........it was steep, and the line of sight distance was almost 400 yds. "Shoot to distance" would have been like 280 yds or something...............long story short, I held for the shoot to distance and was shooting way high. I had to come down another 3" (relative to the rockchuck) to make the hits.

At 280 flat ground I was dead on, but at the angle I was shootin those chucks; I had to hold about 3" below them........dead on wasn't enough.

Not trying to start an argument here, but I have a real life experience that happened about 15 years ago, that made me realize the standard "shoot to distance" or normal cosine type of calculation is not as precise as needed sometimes.

Shooting rockchucks high up on a cliff. Laying flat on my back on basically level ground. Had my rifle proped up on 36" tall shooting sticks that were only about a foot and 1/2 from my armpit..........it was steep, and the line of sight distance was almost 400 yds. "Shoot to distance" would have been like 280 yds or something...............long story short, I held for the shoot to distance and was shooting way high. I had to come down another 3" (relative to the rockchuck) to make the hits.

At 280 flat ground I was dead on, but at the angle I was shootin those chucks; I had to hold about 3" below them........dead on wasn't enough.

You don't reckon the radical change in shooting position had anything to do with the movement of the barrel during recoil what with you being flat on your back against the ground and all that?

I'm certain that it happened just as you say it did and that you did some fine shooting. I just don't think that particular situation is a case for anyone to doubt geometry although it certainly points out that you have to be prepared to adapt to radical shooting situations.

Sbruce, As Micheal explained, there are three general methods, you still need to know angle or cosine, it is in how the cosine is applied, Method one, which is simple triangle method , still helps in closer to 400 yrd on big game, but the least accurate, of the three. In my post I was also relating that the ACI, reads the angle too,

Yes, I suppose that shooting position had some effect on muzzle rise, but that can't really be calculated. I think we should use the most accurate calculations possible because things (just like you mentioned) can and do happen. I don't doubt geometry or trigonometry. In fact; I use both very extensively every day........it's my job Oil companies pay me pretty decent $$'s to hit their targets that are 2 or 3 miles away.

sp6X6,

We actually don't need to know the angle if we know the line of sight distance and the horizontal distance. That's how the cosine value is calculated.

Try this: 282.8 yds (horizontal distance) divided by 400 yds (line of sight distance) and we get .707 not coincidence, .707 is also the cosine of 45 degrees (the angle)..............The shoot to distance (pythagorean theorem) or using the cosine of the line of sight distance both give the same result.

The other method, (which Sierra and NF ballistic programs use) results in a different answer. It is only a couple inches in the rockchuck example, but at least 2 out of my 3" error was due to the simpler and more recognized "cosine of the angle times the distance" method.

When your indicator reads 96, how is that supposed to be used? Are you supposed to dial 96% of your normal dope?.........I've never used one like that.

I see now, the 96 is actually .96 or the approximate Cosine of 15 degrees, .94 being Cosine of 20 degrees, .99 being Cosine of 5 degrees............now I can visualize what you're getting at.

SBruce, Not trying to debate it with you. Your first point, for me as I sit on moutain, I only get line of site with my lazer, so I have to use my cos. dial on rifle to get any more info. And I DONT HAVE a pda type devise,yet.IF I did, that is most accurate, with either cos. or angle as it has inputs for either. And it sound like you are in surveying or some type of area that relates. I BUILD multi mill. homes and have watched the surveyors stake in for me on steep or tight lots. OR I do it myself for easier sites.I did note that triangle method is least accurate. I am forced to use the second which is use your cos. for your drops worked out previous as you noted, and I am taking notes on Micheals , which I think is a more accurate variation.I also want to know how to do sytem w/cos. an simple calc. as I AM trying to cut pack in weight. Thanks for your posts