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Trying understand bullet drop and MOA.

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/11/2015 at 16:29
tpcollins View Drop Down
Optics Journeyman
Optics Journeyman

Joined: January/12/2009
Status: Offline
Points: 384
I have the JBM ballistics program and I'm not sure how to interpret the "bullet drop" and "MOA drop" columns. I have a scope with the 4A reticle and the subtend from the crosshair to the top of the bottom post is 8.3" (or 7.9 MOA) at 100 yards. With a 100 yard zero, I would like to use the top of the post as a holdover but I'm not sure which column to use. Do I use the drop yardage for 8.3" which could be 300 yards for example, or use the 7.9 in  the MOA column ( I always thought that was "clicks up") which might be 450 yards or so?  Thanks.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/11/2015 at 19:15
Sgt. D View Drop Down
Optics Master Extraordinaire
Optics Master Extraordinaire

Joined: February/20/2008
Location: North Carolina
Status: Offline
Points: 3831
I can't talk the detailed talk that you are askin about. There are some here who can and I hope they will as I always learn something when they do. But, I can tell you that they can only advise you in theory. Because unless you are fortunate to be one who's "ACTUAL" trajectory matches your program or scope set up you will have to "ACTUALLY" put rounds on paper and then go with whatever your scope happens to show you. If you are asking for the sake of understanding the program then I too wait for someone to speak up. But if you are heading to the range then you will have to let the little round holes tell you what you can count on. In some instances you can adjust your load recipe to come close to those programs. Good Luck!! 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/12/2015 at 07:31
8shots View Drop Down
Optics Jedi Knight
Optics Jedi Knight
Lord Of The Flies

Joined: March/14/2007
Location: South Africa
Status: Offline
Points: 5944

1 MOA = 1.047 inches at 100 yds

7.9 MOA is 8.3 inches at 100yds.

So if the subtend is 7.9 MOA or 8.3 inches at 100 yds, the zero yardage point would be identical for both, both would be at say 300yds.

You can therefore use either inches or MOA column, they give the same zero point.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: January/15/2015 at 11:53
koshkin View Drop Down
Dark Lord of Optics

Joined: June/15/2004
Location: United States
Status: Offline
Points: 11801
Switch to angular units (MOA or mrad) and think of your holdover in terms of angular units.

Thinking about holdover in terms of inches will get you into trouble sooner or later.  Sooner in this case, as evidenced by your post.

If the MOA drop column says that 7.9MOA is at 450 yards, then that is the distance where the top of the post is going to be the right aiming point.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/10/2015 at 17:15
trentsmill View Drop Down
Optics GrassHopper
Optics GrassHopper

Joined: February/10/2015
Location: Virginia
Status: Offline
Points: 2
Here is a link to a great article and YouTube Video about Mil and MOA.

I use the Ballistic app for my iPhone. It is awesome. It does all the calculations for you. I highly recommend it.
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