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Improved Angle Cosine Indicator

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Unread 10-20-2004, 05:45 PM
Posts: n/a
Re: Improved Angle Cosine Indicator

Gentlemen: It appears that we are all focused, if not hyper-focused on this issue as well as obtaining the same level if not an extreme level of accuracy. When I originally designed the ACI it was for Military Snipers. Military Snipers are trained to round up in five degree increments and were using protractors as their means of measurements. This is a far cry from the ACI. In any regards, as you know, the cosine numbers are in five degree increments so if the shooter desires to utilize angles, he/she can count up. Although, the cosine numbers are in place to eliminate the step of going to your data book to obtain the cosine number (SOP).

Commingle the ACI with good ballistic targeting software such as Exbal, or Sierra’s infinity and 1st shot hits on target, and at distance is a reality. There are military personnel around the Globe that are making 1st shot hits at 1700 yards utilizing the .338 Lapua, good glass and an ACI.
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Unread 10-20-2004, 05:50 PM
Junior Member
Join Date: Apr 2004
Location: Mission Hills CA
Posts: 27
Re: Improved Angle Cosine Indicator

Jeff, I have Snipertools ACI's on both of my competition rifles, one, an Accuracy International 308, the other a tactical 6.5-284 in a A5 Mcmillan stk with all the bells and whistles.

I bet you $100 that I can hit a man sized target at 800 yrds center mass at any angle up hill or down hill using SniperTools ACI with either of my rifles, you pick the hill and the range and see if I'm bull shiting.

I hope your body armor works really well [img]images/icons/wink.gif[/img] [img]images/icons/grin.gif[/img] [img]images/icons/grin.gif[/img]

I've pulled off cold bore shots at at that range many times using ex ball and the ACI, And I can guarantee you this, if the wind is not howling, the elevation of the shot will be dead nut every time. [img]images/icons/grin.gif[/img]

Just wondering, do you own a ACI ????? I have placed over 200 center of mass shots at that range with mine [img]images/icons/grin.gif[/img]
He who laughs last, laughs the hardest.
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Unread 10-20-2004, 06:00 PM
Platinum Member
Join Date: Aug 2003
Location: NC, oceanfront
Posts: 4,226
Re: Improved Angle Cosine Indicator

The ACI used to be offered in degrees. I believe it was discontinued in favor of cosine increments(no software needed). Ward was kind enough to sell me a couple ACI's with the older degree windows installed when requested(10deg incr). I also have 2 others in cosine increments(5deg incr).
I really like the darn things, great overall design. I have many kills using it as part of my system -routine.
I just wish It had alittle better resolution, because sighters are not an option in real world shooting at angles. Right?
I get one shot. If I miss, lucky prey lives another day. Thats my rule. [img]images/icons/smile.gif[/img]

[ 10-20-2004: Message edited by: Mikecr ]
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Unread 10-20-2004, 06:04 PM
Silver Member
Join Date: Sep 2004
Location: Southwestern Montana
Posts: 294
Re: Improved Angle Cosine Indicator

Is there a rule of thumb that can be applied and get good results? I was going to ask this very thing today but this seems to fit right in here. How does the ACI work if shooting uphill? I was wondering how much stuff you can tape to the stock or in the scope cover. I imagine it would be tough to find a place to shoot at very many angles to get actual numbers. I like the KISS rule for most things so a thumb rule is my preference. I am not shooting for competition though so close would be ok.
If you're gonna be dumb you better be tough.
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Unread 10-20-2004, 06:12 PM
Platinum Member
Join Date: Aug 2003
Location: NC, oceanfront
Posts: 4,226
Re: Improved Angle Cosine Indicator

If your not wanting to split hairs at really, really long ranges, the ACI in it's current form will work great for you. You can follow the link to the ACI site and read about it's use. Basically you use it to caclulate a corrected range for the angled shot. Then apply that corrected range when looking up your drop.
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Unread 10-20-2004, 08:42 PM
Silver Member
Join Date: Aug 2003
Location: McKinney TX
Posts: 408
Re: Improved Angle Cosine Indicator


I do not doubt your abilities behind the trigger, nor do I doubt my abilities behind the trigger. A lot of it comes down to how much training and work you put into this sport

I spoke in terms of general statistics. Yes, trained professional who practice these disciplines can often make these type shots, excluding shots in strong winds. But in general most folks cannot make a first shot hit on a body sized target at 700 yards or greater.

I use my mil-dot master with a small lead fishing weight tied to a piece of fly fishing line for my angle indicator. I have one of the original mil-dot masters that the late Bruce Robinson gave me many years ago right after he came out with it. I took a sharpie and added additional degree lines which I fit my needs and requirements. I then put a piece of transparent tape over the sharpie marks so I would not wear them off over time. I also add a ballistic card to the back of the Mil-Dot master that matches my typical location and conditions I'll be shooting at. My system is simple and works for me.

If you ever get down Texas way let me know. Maybe we can meet and shoot for an afternoon and enjoy a good steak afterwards.

Good luck and good shooting! [img]images/icons/grin.gif[/img]

[ 10-20-2004: Message edited by: Jeff In TX ]

Mathew 5:16

Distance is not an issue, but the wind will make it interesting!
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Unread 10-20-2004, 11:43 PM
Join Date: May 2001
Posts: 6,518
Re: Improved Angle Cosine Indicator

Guys, you are right. Ward concedes this fact and even has a very detailed explanation on his website of the reasons why there are limitations to the cosine method af adjustments.

If you want a method that works in ALL conditions don't use the cosine method. However, this simple method has a valid use for many of us long rangers. In fact, I bet the range/angle conditions present for 75% of our members would be handled accurately all the time. Only when you get to a certain combo of longer range and steeper angle does this simplest method lose practical accuracy. I plan to be proficient in both methods and use whichever one makes most sense in the terrain I plan to hunt.

The cosine method is plenty good with my 7mm Dakota and .750 BC bullet, for example, at a combo of 600yds and 15 degrees. I have hunted in Montana, New Mexico, Old Mexico, Alaska, Kansas, Wyoming (next month) and Colorado. I don't remember ever having had a shot opportunity steeper than about 10 degrees. The steepest terrain I hunted in was the Wrangell Mountains of Alaska where I expected a steeper shot at a Dall's sheep but never got a shot at all.

On my next hunt...this weekend in the Missouri River Breaks region of Montana...I will keep track of the angles I encounter with my Leica Laser Locator Plus. I doubt I'll have an animal out there at more than 15 degrees. At 600 yards there just is no significant difference in the methods used.

In order to force myself to learn the more accurate method while on this trip I am leaving my ACI home and will have an adjustment chart along instead...using the "Improved Rifleman's Rule" as outlined in the William T McDonald article on Ward's website. Then, while on the hunt I will pay more attention to what the angles may reallistically be in that terrain and decide at the end of the trip whether my own future hunting conditions will likely ever benefit from the IRR method. If not I am going to buy one of Ward's new and improved models.

[ 10-20-2004: Message edited by: Len Backus ]
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