Monday, September 01, 2008

Making the Long Shot

The Armed Canadian teaches you how to adjust for the long shot.

We won’t discuss 100 or 200 yards here. As I said, my rifle is zeroed at 200 yards. Where I put the crosshairs is where the bullet will theoretically land at that distance. 300 yards is where it starts to get interesting.

Consulting the ballistics table for the 139gr boat tail round I am shooting (yes, they break it down by weight and bullet type, each fly differently), I read a drop of 8.4 inches at 300 yards. Great! Assuming no wind and a perfect shooting, my rounds will be clumping 8.4 inches below the bullseye if that is where I am aiming. If I want to put the crosshairs on the bullseye and hit it, I need to adjust the scope so it raises the point of impact to meet the point of aim. In other words, I need to raise it by 8.4 inches.

That’s where the calculator comes into play.

8.4 inches is not a value in MOA. We need to translate it into MOA. We do this by a very simple formula:

deviation in inches / (range in yards / 100)

This works for the known ranges where you have drop figures for. For those that you don’t, you need to guess. What this formula does is translate your drop in inches into drop in MOA. Once you have that, you can adjust your scope. So if we plug in 8.4 inches and 300 yards, we get a value of 2.8 MOA.

Since my scope is adjusted in 1/4 MOA increments, we multiply that number by 4 (or divide by 1/4 or .25). That gives a value of 11.2. This is the number of clicks in “Up” direction I need to dial into the elevation turret on the scope to bring the rounds onto the bullseye.

You do the same thing to account for wind. If the wind is blowing your rounds 2 1/4 inches to the right at 300 yards, you have a deviation of 0.75 MOA. For a 1/4” MOA scope, this means you dial in 3 clicks of “Left” adjustment to compensate.

Hat tip Firearms & Freedom.

(5) Comments
Posted by Owen at 1701 hrs
Firearms

  1. This is good stuff.  Do you do a lot of shooting?

    Posted by .(JavaScript must be enabled to view this email address) on September 01, 2008 at 2055 hrs


  2. Not as much as I’d like.

    Posted by Owen on September 01, 2008 at 2108 hrs


  3. I just watched the “Extreme Marksman” special from the History Channel that I had taped.  The Army snipers hit a target from 1,000 yards away in a quick 5 shot burst plus they are dealing with a 37 FOOT drop, just unreal.

    Posted by Benjamin on September 01, 2008 at 2112 hrs


  4. At those ranges, your major concern is not the drop but the wind. Every good long range marksman knows the number of clicks in 50 yard increments out to their maximum effective range to compensate for bullet drop.

    What separates the men from the boys is your ability to accurately read wind and mirage at long range and apply those observations in quarter, half or full value windage corrections based on what you see.

    Posted by .(JavaScript must be enabled to view this email address) on September 02, 2008 at 1155 hrs


  5. I’m not sure on optics (where the reticle “sight” and target are in the same optical plane), but I know there’s an excellent Jim Owens piece on how you actually need to take the adjustment in MOA and halve it with iron sights.  That has been my experience in Highpower shooting so far - halve the adjustment and you’ll get there without chasing your zero around in circles.

    I don’t have to worry about drop or windage (I shoot at West Bend Barton Sportsman’s Club) because we shoot at reduced targets on the 100 yard line, instead of the 200, 200, 300, and 600 yard distances of an actual relay.

    Posted by Mike Gallo on September 02, 2008 at 1629 hrs


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