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# Cosine or degrees which do you prefer?

#8
11-19-2009, 12:24 PM
 Silver Member Join Date: Jan 2005 Posts: 338
Re: Cosine or degrees which do you prefer?

Using the degree of angle is far more accurate than COS !! Here is an example from my Ebal charts for my 7mmRHB fireforming loads.

168 berger @ 3255 fps-- starting 3" high at 100yds, takes 16 min. IPHY elevation change at 1000yds. Shooting at a 30* angle the COS tells you 87% or 870 yds shot equivalent ( 12 min.IPHY)

Now going to Exbal and hitting the angle shooting function on ECCEL and looking at the chart for a 1000yd shot at 30* and it gives you 14.25 min. IPHY or the equivalent of 925 yds to make the shot !! This is because you still need to take into account the time of flight and the effects of air drag on the bullet for the entire distance ( 1000yds )----RHB
#9
11-19-2009, 12:51 PM
 Official LRH Sponsor Join Date: Mar 2007 Posts: 634
Re: Cosine or degrees which do you prefer?

RHB,

Multiplying the range by the cosine provides a very rough estimate. However, if you multiply the bullet drop by the cosine, it provides a much closer estimate.

Ultimately calculating a trajectory with degrees is the most accurate way, but the estimate provided by multiplying drop by the cosine is quite close.

As an example, consider a typical trajectory that's -314.3" low at 1000 yards for a level fire scenario. Incline the trajectory by 30 degrees, and the drop is now -271.4". If you approximate the drop by: -314.3" * cos(30) the answer is -272.2", which is only 0.6" different than the direct calculation.

-Bryan
#10
11-19-2009, 03:37 PM
 Silver Member Join Date: Jan 2005 Posts: 338
Re: Cosine or degrees which do you prefer?

You're absolutely correct Bryan. I guess I should have read your posts more closely. We have discussed this subject many times on LRH so when I saw ACI my brain just jumped ahead of what was being said. My mistake. However, I still prefer to use an angle chart and not have to do math in the field. Since my range finder gives me the degree of angle, I find it much more simple to use the Exbal angle chart ( unless Groupers there with his PDA )to make my shots!---- RHB
#11
11-19-2009, 11:11 PM
 Silver Member Join Date: Feb 2009 Location: Truckee Posts: 293
Re: Cosine or degrees which do you prefer?

Why not both?
#12
11-23-2009, 04:17 AM
 Platinum Member Join Date: Jul 2007 Location: Arkansas (Home of Record) Posts: 1,929
Re: Cosine or degrees which do you prefer?

Quote:
 Originally Posted by theodore Why not both?
Why not both...what? Do you mean to have a tool that gives both readings?

As for the original post, I prefer a cosine reading. That way I don't have to carry a conversion chart, need to convert that angle into a decimal. The only reason I can see needing degrees is that your ballistics program only allows you to use degrees. I use JBM at the house and I believe it will only let you inpute degrees. I can use cosine with exbal. If exbal goes down in the field I would multiply my drop for a given range (Improved Rifleman Method) by the cosine to get the corrected for gravity drop. The ballistic programs are supposed to be the most accurate due to effects of time of flight and such.
#13
11-23-2009, 10:24 AM
 Silver Member Join Date: Feb 2009 Location: Truckee Posts: 293
Re: Cosine or degrees which do you prefer?

Quote:
 Originally Posted by Bravo 4 Why not both...what? Do you mean to have a tool that gives both readings? .....
Yes, Horus Vision have ASLI (Angle Slope Level Indicator) reads both cosine and degrees.
#14
11-23-2009, 10:45 AM
 Platinum Member Join Date: Jun 2009 Posts: 1,654
Re: Cosine or degrees which do you prefer?

Quote:
 Originally Posted by theodore Yes, Horus Vision have ASLI (Angle Slope Level Indicator) reads both cosine and degrees.
You can see it at WWW.MountsPlus.com

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