How do I calculate the correct MOA drop?

tpcollins, MOA is not the rough 1" at all ranges, that is only at 100 yards.

Once you get out to 189 yards each MOA measurement equates to about 1.9". So your POA will be 8.3 MOA above your POI. Doing the math your POI will be: 1.9" * 8.3 MOA = 15.77" of drop below your POA (which is your 127 yd zero).

189 yards - 127 yards = 62 yards

That is how Big Al calculated that in the last ~ 60 yards your round will be dropping ~ 15".
 
How do we get 15" or 17" drop when the 8.3 MOA on my ballistics chart aligns with 189 yards? (I shortened the increments to fit in the page). I can see a 15" or 17" drop if I use the center of the crosshair but not the heavy edge of the vertical post.


Rang
yds Path

10 -0.7
20 0.0
30 0.7
40 1.2
50 1.5
60 1.8
70 1.9
80 1.9
90 1.8
100 1.5
110 1.1
120 0.5
130 -0.3
140 -1.2
150 -2.2
160 -3.5
170 -5.0
180 -6.6
190 -8.4
200 -10.5
 
Well, you were saying that the post was 8.3 MOA below your crosshair and that it was your POI at 189 yards.

If that is indeed the case, then there is 15" of drop at that distance. If the top of the post is not actually your zero at 189 yards then your earlier post was misunderstood by all of us that read it.
 
How do we get 15" or 17" drop when the 8.3 MOA on my ballistics chart aligns with 189 yards? (I shortened the increments to fit in the page). I can see a 15" or 17" drop if I use the center of the crosshair but not the heavy edge of the vertical post.


Rang
yds Path

10 -0.7
20 0.0
30 0.7
40 1.2
50 1.5
60 1.8
70 1.9
80 1.9
90 1.8
100 1.5
110 1.1
120 0.5
130 -0.3
140 -1.2
150 -2.2
160 -3.5
170 -5.0
180 -6.6
190 -8.4
200 -10.5
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I just went back. We read your earlier post right, you just aren't understanding what your ballistic chart is telling you.

An 8.3 MOA drop on my ballistics chart indicates an estimated POI on the bull at 189 yards.
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Your chart is telling you that at 189 yards your round will be hitting 8.3" low. That is actually about 4 MOA. Your chart is not giving you the drop in MOA, it is giving it in Inches. Those two are only roughly equal at 100 yards.
 
Your chart is telling you that at 189 yards your round will be hitting 8.3" low. That is actually about 4 MOA. Your chart is not giving you the drop in MOA, it is giving it in Inches.
Click to expand...

Yep.
8.3 MOA at 190 yards is about 16.5 inches.
 
You are looking at the inches drop on your table and thinking that it's MOA. At 189y the table says you have 8.5" drop. At 189 yards that is less than 8.5 MOA.

Actually 8.5" x 100y / 189y = 4.5 MOA (using the 1 MOA = 1" @ 100y approximation)

It is a little tricky because you have to solve backward to find what distance will give you 8.5 MOA when the table only gives inches and yards. Can you set the calculator to give you MOA instead of inches? Or you could use the above equation to guess and check values from your table until you converge on an answer. But we do know for sure that 8.5 MOA is something past 200 yards.

Remember the further this gets away, the smaller your target will be in the scope and the less likely you will be able to visually estimate hold-over to stay on target.
 
My calculator is giving about 230y to get to 8.5 MOA. But I was guessing at MV and BC to match your table.

Another thing to keep in mind is wind. A 10MPH crosswind will put you about 18" off the POA at that distance.
 
tpcollins, I suspect that you have not been taught what moa means. So I shall attempt an explanation. MOA stands for minute of angle. A circle is divided into 360 degrees. Then divide 1 degree into 60 minutes. That is a fairly small measurement of angle. To demonstrate one minute of angle take 2 strings tied together and hold it at your barrels muzzle. Go out to 100 yards and hold them 1 1/8 inch apart (1 moa). Continue out to 200 yards keeping the spread at 100 yards 1 1/8 you have to hold 2 1/4 inches at 200 (still1moa) at 300 yards 3 3/8 inches. Basically the farther away it is from you the more it measures. Your scope subtends 8.3 moa to the post so at 200 yards it subtends almost 16 1/2 inches. So with your load hold the center of the thin reticle where you want the bullet to impact. ( the average deer is about 18 inches from top of hair on the back to bottom of hair under the chest ) at 200 yards put the cross hair on its hairline on the back and shoot. Dead deer.
 
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Well I do understand that 1 MOA at 100 yards is 2 MOA at 200, etc., etc. What I don't understand is if at 100 yards, the POI is 1.5 high at 100 yards, and dead center at 127 yards, that it will drop an additional 17" or so over the next 62 yards. My brother-in-law has a different ballistics program that shows the actual bullet trajectory over distance - maybe that will help.

I'm going to have to go to the field, mark off 189 yards, put up the biggest target I can find and see where it hits with the edge of the post aimed at the bullseye. I'm going to have to buy a book on MOA so I can understand it completely. Thanks.
 
I'm going to have to go to the field, mark off 189 yards, put up the biggest target I can find and see where it hits with the edge of the post aimed at the bullseye. I'm going to have to buy a book on MOA so I can understand it completely. Thanks.
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All this time I thought you had a very specific distance you new you would be shooting . Thats why you are zeroed at 127yds. May I ask why 127 and not 100yds .

Here is a video about MOA http://www.youtube.com/watch?v=VA2PZBD5Tjg&feature=relmfu
 
Tpcollins, it will not drop 17" at 190 yards. Go back and read the earlier posts again. It will only drop about 8" as your ballistic chart says.

Sent from my HTC One X
 
Metal god - I chose the 1.5 high at 100 yards for a reason. At that trajectory, the highest part of the trajectory is 1.9" at 63-86 yard range. The drop for 1.9" is at 147 yards. So I can shoot at a deer out to 147 yards, aim at the center of the vitals, and hit a 4" circle.

If I sight it in at 100 yards, the highest part of the trajectory is only .9" from 55-71 yards but the same 1.9" low is at 127 yards. I want to aim at the center of the target.

All around - as I read the posts it seemed to me that the answers were going in different directions - maybe it's just me.
 
All around - as I read the posts it seemed to me that the answers were going in different directions - maybe it's just me.
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They are all saying the same thing, it is just your current understanding of MOA is making it difficult. Let's try to start over and reteach you the basics of what MOA actually is:


What you need to understand first is that MOA = MOA, regardless of range.

1 MOA at 100 yards = 1 MOA at 200 yards = 1 MOA at 300 yards etc....

A basic understanding of the conversion of MOA to inches is that 1 MOA = ~1/100 * range.



As an example I will calculate 1 MOA at 200 yards:

1 MOA = (1/100)*(200) = 2"

And now for 500 yards:

1 MOA = (1/100)*(500) = 5"



Now if we go back to your thought of 189 yards:

1 MOA = (1/100)*(189) = 1.89"


Now, you chart said that you would be hitting 8.3" low of your POA at that range. To calculate that drop in MOA you have to divide your total drop (8.3") by what the value of 1 MOA is (in inches).

It would look something like this:

8.3" / 1.89" (which is 1 MOA) = 4.39 MOA
 
I keep confusing the two - here's Plan B:

Here is the link for the Swarovski 4A reticle with the 8.3" sub tension at 100 yards.

http://www.swarovskioptik.us/upload/media/media/33/abdeckmasse_z5_z3_9spr[968].pdf


Here is my ballistic data:

Bullet Dia - .451"
BC - .210
Bullet Wt - 250gr
Muzzle Vel - 1850 fps
SD - .176
Zero Range - 127 yards
Interval - 1 yard
Max Range - 200 yards
Sight Ht - 1.504"
Clicks/MOA - 4
Temp - 40 degrees F
Altitude - 1000 ft


At 100 yards, the bullet impacts 1.5" high using the center of the crosshair. If I use the heavy edge of the post as my aiming point, at what yardage would the bullet hit dead center of the bullseye? If I can get that exact distance, I can reverse engineer the answer and understand how it works. Obviously I'm plumb dumb instead of being just some dumb. Thanks.
 
I get it. Actually rereading the posts and SSA and Eric75 mentioned adding 1.5 to 8.3 and that was my original thinking but I didn't know how to interpret the info. On another forum I got my ass shot off for using inches when I should have been using MOA. So by mistake, I went with MOA ere and actually I should have been using inches.

Using the post gives me a POI of about 235 yards, which someone indicated, and a lot further than I want to shoot a ML. I'll just limit my shots to 150 yards and enjoy looking thru the scope! Thanks.
 
Glad we could help a little. When using a muzzleloader there really is no need to discuss MOA 99.99% of the time. Heck, for a vast majority of centerfire rifle shooters there is no need to have an understanding of MOA.


It really becomes more of a tool when you get into longer range shooting. Good luck on your upcoming hunts. Hunt hard, shoot straight, and put some good meat in the freezer!
 
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