Correcting ballistic drop at different zeros?

[drcrea]

First, let me start by saying I'm rather new to the long distance game so my apologies if my terminology is wrong. I also apologize if this is obvious to others. I don't get it and I couldn't find any sort of explanation searching the interweb and u-tube. Maybe I'm just not asking the question right?

What I'm trying to understand is how to calculate ballistic drop when you have a different zero on your rifle from what the ballistic chart has for the ammunition? Yes, I understand that I can use a ballistic calculator/app, but what I'd like to know is how to make the adjustment manually using good old fashion math. Trying to understand how the math works.

Here is my example, PMC 308B, FMJ-BT, 147gr / bc 0.398

• Muzzle: -1.5
• 100 Yds: +1.88
• 200 Yds: 0
• 300 Yds: -8.03
• 400 Yds: -23.29
• 500 Yds: -47.11

So if I have my rifle zeroed at 200yrd, I would have ~-47 inches for drop. Cool! But I have my rifle zeroed at 100yrd and I know the drop is closer to ~-59 inches from experience. How do I do the math to make this correction for a different zero?

 

[Rio Precision Gunworks]

There’s pretty much no reason to know how or to do this. That’s why you won’t see anything online.

 

[_Windrider_]

Like ^ said. There is no reason to do this or know that maths.

 

[Marine52]

First, let me start by saying I'm rather new to the long distance game so my apologies if my terminology is wrong. I also apologize if this is obvious to others. I don't get it and I couldn't find any sort of explanation searching the interweb and u-tube. Maybe I'm just not asking the question right?

What I'm trying to understand is how to calculate ballistic drop when you have a different zero on your rifle from what the ballistic chart has for the ammunition? Yes, I understand that I can use a ballistic calculator/app, but what I'd like to know is how to make the adjustment manually using good old fashion math. Trying to understand how the math works.

Here is my example, PMC 308B, FMJ-BT, 147gr / bc 0.398

• Muzzle: -1.5
• 100 Yds: +1.88
• 200 Yds: 0
• 300 Yds: -8.03
• 400 Yds: -23.29
• 500 Yds: -47.11

So if I have my rifle zeroed at 200yrd, I would have ~-47 inches for drop. Cool! But I have my rifle zeroed at 100yrd and I know the drop is closer to ~-59 inches from experience. How do I do the math to make this correction for a different zero?

You can do it fairly easy but it’s not something regularly done since most serious shooters have ballistics apps.

1. Convert the inch figures to MOA or Mils for each yardage (for example 1.88” at 100 yards is 1.80 MOA or .52 Mils)

2. If using MOA, zero out the 100 yard MOA number by subtracting 1.80 from that figure and then subtract 1.80 from each other yardage MOA number. This Is your 100 yard zero angular correction in MOAs. You can then convert these back to inches if you want. If you use Mils, the procedure is the same

 

[Mike Casselton]

If you really just have to have the info, a lot of the old reloading manuals have charts in the back for just that purpose.

 

[Enough Said]

Irrelevant once you have established a solid zero.