Use of Angle Cosine Indicator (ACI)

[Lexington]

If the shooting position and the target are on the same horizontal plane, the ACI reads 0. As elevation is dialed onto the scope, the barrel is raised relative to the target. So even if the shooting position and target are on the same horizontal plane, an elevated barrel (and scope rail) will cause the ACI to read anything but zero. I could stay in my same position and engage targets at different ranges, and the elevation will change with each one.

In other words, it appears the shooter sets the ACI for zero at a specific known horizontal distance, and that dialing elevation from the same position to several different targets at varying distances will make the ACI useless (or cumbersome to work with). Correct?

 

[Mendy300wm]

You're over thinking this too much...
Step one find the range to target
Step two find the cosines off your ACI multiply that number by the line of sight distance to target
Step three take that corrected range and adjust your scope accordingly
Step four make windage adjustment for the line of sight distance
Step five.... KaaaBoom... Ding

 

[Lexington]

I understand Steps 1 through 5.

Let's say I have everything, including the ACI, set up for a 300yd. shot. Steps 1 through 5, bang.

Now I stay in the same position and engage a 600 yd. target on the same horizontal plane as me and the 300 yd. target. But I have to dial elevation onto the scope to shoot the 600 yd. target. So, the barrel is raised as a result of adding elevation and the ACI rotates into a reading of an uphill shot. That's what I'm getting at.

 

[Papa Zero Three]

+1 on You are overthinking this. Mendy answered your 2nd shot question. You would repeat the steps again. Assuming your 2nd tgt range was 600 yds, you already know the angle so again, figure for the corrected distance and dial that dope on your gun and click, bang.

 

[Blanman]

Trust me when I say this, it's not going to make a difference. You have to get to a pretty steep angle and a good distance before the shift becomes substantial.

 

[Bigwheels]

I'm not going to do the actual math but your main problem is in thinking a few MOA is going to be equal to several degrees. Even 100 moa isn't 1 degree angle.

 

[Morgan321]

Lexington: You are correct. But it is imperceptibly small. If you dial in, say 60 moa of elevation that is 1 degree. The cosine of 1 degree is 0.9998. So if you were shooting 1000yd your "effective" range will be changed by 0.2 yards. I can't tell the difference in 20yd at 1000yd, much less 0.2 yards.

Bigwheels: 60 moa is 1 degree.

 

[Lexington]

Lexington: You are correct. But it is imperceptibly small. If you dial in, say 60 moa of elevation that is 1 degree. The cosine of 1 degree is 0.9998. So if you were shooting 1000yd your "effective" range will be changed by 0.2 yards. I can't tell the difference in 20yd at 1000yd, much less 0.2 yards.

Bigwheels: 60 moa is 1 degree.

Got it. I was letting theory get in the way of practical math. I'm GTG now.

 

[Bigwheels]

Morgan. Thanks, I knew it was a lot, but just didn't spend the brain power on it. The play offs are on.

 

[M82A1]

This is what I don’t understand. Shooting up reduces range due to gravity. Shooting down increases range due to gravity. Why does the angle cosine indicator have the same numbers above and below zero?

 

[Lowlight]

This is what I don’t understand. Shooting up reduces range due to gravity. Shooting down increases range due to gravity. Why does the angle cosine indicator have the same numbers above and below zero?

Because you are wrong.

Up or down is the same, there is a tiny, I mean tiny offset for the gravity of a downhill shot but regardless or up or down you hold low

You woke up a very old thread, but do you think it was different the tool would be designed the way it was?

Super simplified but

 

[M82A1]

I don't think I'm wrong. If you point your rifle up in the air (+90 degrees), and shoot, the bullet will eventually stop and come back down, since gravity is pulling it down. If you point your rifle down (-90 degrees), the bullet will keep going until it hits the center of the Earth (if there's a deep enough hole). How does the Angle Cosine Indicator play together with gravity?

 

[Lowlight]

That was a bit harsh,

I will edit this to say, Wrong, on so many levels, but thanks for reviving a necro thread

 

[_Windrider_]

I don't think I'm wrong. If you point your rifle up in the air (+90 degrees), and shoot, the bullet will eventually stop and come back down, since gravity is pulling it down. If you point your rifle down (-90 degrees), the bullet will keep going until it hits the center of the Earth (if there's a deep enough hole). How does the Angle Cosine Indicator play together with gravity?

what If your LRF doesn’t give you the THR but just the LOs range, you need to know what to multiply by to get your hold (elevation, is gravity). Sam if you are using a ranging formula.

 

[Lowlight]

Plus 45 Degree angle at 1000 yards 5.2
Minus 45 degrees at 1000 yards 5.1

0 Angle = 7.8

All

 

[M82A1]

Wow! Sorry about the dumb question. I will make sure they are more highly researched first.

 

[Lowlight]

It's always the 50 cal fans...

So you know a 90-degree shot is a mechanical offset problem, not a gravity one. At Rifles Only we had a 90-degree stage off the tower, it was 21ft straight down and you used your 700-yard dope for the mechanical offset

Off the top rail, straight down 700 yard dope to hit a 1/2" dot

 

[_Windrider_]

It's always the 50 cal fans...

So you know a 90-degree shot is a mechanical offset problem, not a gravity one. At Rifles Only we had a 90-degree stage off the tower, it was 21ft straight down and you used your 700-yard dope for the mechanical offset

Off the top rail, straight down 700 yard dope to hit a 1/2" dot

No shit eh, so this is why I can never hit anyone below me on call of duty!!!

 

[Lowlight]

In Call of Duty you need the coolest of the 9mm subguns to be the most effective or use a Cheytac M200, otherwise, no killie baddie

 

[Basher]

No shit eh, so this is why I can never hit anyone below me on call of duty!!!

gEt GuD, bRuH!

Frank’s close, but it’s a 10mm subgun you want. Or the Kar98K. Or whatever Phil Velayo’s using, he’s tearing it up according to his FB posts.

 

[M82A1]

Thanks Frank. We’re good.

 

[Long Range 338]

I don't think I'm wrong.

This is where things went sideways. Its not a problem to ask a question, even if it someone feels it is a dumb question. It becomes a problem when you decide to become an ass and argue with the professional who is trying to explain it to you.

I'm still trying to understand what shooting straight up or straight down has to do with shooting at angles? When shooting at angles its about the horizontal distance. Straight up and straight down equals zero horizontal distance.

 

[308pirate]

I understand Steps 1 through 5.

Let's say I have everything, including the ACI, set up for a 300yd. shot. Steps 1 through 5, bang.

Now I stay in the same position and engage a 600 yd. target on the same horizontal plane as me and the 300 yd. target. But I have to dial elevation onto the scope to shoot the 600 yd. target. So, the barrel is raised as a result of adding elevation and the ACI rotates into a reading of an uphill shot. That's what I'm getting at.

The angle that the barrel is elevated to when adjusting sight elevation is so trivial that there is zero effect to your trajectory from it.

I'll be like the 10th person to tell you that you're overthinking it.

If you're feeling froggy, do the math to figure out the barrel inclination induced by adding 600 yd elevation (4 mils +/- for most cartridges) and then do the trig to compare the LOS range to the LOB (line of bore) range.

 

[Long Range 338]

The angle that the barrel is elevated to when adjusting sight elevation is so trivial that there is zero effect to your trajectory from it.

I'll be like the 10th person to tell you that you're overthinking it.

If you're feeling froggy, do the math to figure out the barrel inclination induced by adding 600 yd elevation (4 mils +/- for most cartridges) and then do the trig to compare the LOS range to the LOB (line of bore) range.

Actually in this example the scope is compensating for this when the distance is dialed.

 

[308pirate]

Actually in this example the scope is compensating for this when the distance is dialed.

Please explain how..... and show your work.

 

[Long Range 338]

[QUOTE="308pirate, post: 8417140, member: 113603"
Please explain how..... and show your work.
[/QUOTE]

Not even gonna attempt that (and I wasn't disagreeing with you even if it sounded like it). But to say that the minor amount of barrel inclination is factored in when you figure you dope is obvious. At 100 yards you zero, dial up to lets say 800 yards, and boom, gong! Pretty much the purpose of the optic. Just stating the same conditions as the OP with shooter and targets all on the same horizontal plane.

 

[Lowlight]

Look at the date, this original thread was from 2014

You can't answer the original content those guys are probably not here, LOL

 

[_Windrider_]

gEt GuD, bRuH!

Frank’s close, but it’s a 10mm subgun you want. Or the Kar98K. Or whatever Phil Velayo’s using, he’s tearing it up according to his FB posts.

I put those numbers up in HC Domination as well. I mostly play HC S&D and warzone.

 

[M82A1]

This is where things went sideways. Its not a problem to ask a question, even if it someone feels it is a dumb question. It becomes a problem when you decide to become an ass and argue with the professional who is trying to explain it to you.

I'm still trying to understand what shooting straight up or straight down has to do with shooting at angles? When shooting at angles its about the horizontal distance. Straight up and straight down equals zero horizontal distance.

I wasn't trying to become an ass. I had a real question I was seeking and answer to. My question was about how the ACI works with bullet drop, and if there's a difference between shooting at the same angle upwards vs downwards. I made two mistakes looks like. 1) I revived an old thread, because I didn't want to start a new thread about a topic already discussed, and 2) I asked a question which turned out to be a stupid question.

Expect better results from me in the future.

 

[Basher]

I put those numbers up in HC Domination as well. I mostly play HC S&D and warzone.

Yeah, I only play in the HC lobbies, other than Gunfight and Plunder (freaking LOVE Plunder!). I’m pretty good, but not reliably good. I’ll have several amazing rounds, then get my A handed to me all of a sudden. Doh!

Sorry to play into the thread derail!

 

[_Windrider_]

I wasn't trying to become an ass. I had a real question I was seeking and answer to. My question was about how the ACI works with bullet drop, and if there's a difference between shooting at the same angle upwards vs downwards. I made two mistakes looks like. 1) I revived an old thread, because I didn't want to start a new thread about a topic already discussed, and 2) I asked a question which turned out to be a stupid question.

Expect better results from me in the future.

We’ve all been there. It’s a right of passage

 

[M82A1]

Thank you everyone for the info.

 

[Lexington]

Look at the date, this original thread was from 2014

You can't answer the original content those guys are probably not here, LOL

I'm still here. And I can do trigonometry and stuff.

 

[M82A1]

I also know triggernometry.