How To Compensate For Longer Distances With a Scope.... (rifle, best, Winchester)

[WhipperSnapper 88]

I'm sure this will sound like a dumb question, but I'm new to long range carbine shooting.

I have my rifle scope zeroed at 100 yards, so my question is, what if I'm shooting at a target at about 170 yards? How would I know how many clicks I would have to move the elevation up?

I thought I heard some kind of formula for figuring this out before, since gravity has the same rate of pull on all objects, but I don't remember.

Any advice is appreciated.

[Gungnir]

Originally Posted by WhipperSnapper 88

I'm sure this will sound like a dumb question, but I'm new to long range carbine shooting.

I have my rifle scope zeroed at 100 yards, so my question is, what if I'm shooting at a target at about 170 yards? How would I know how many clicks I would have to move the elevation up?

I thought I heard some kind of formula for figuring this out before, since gravity has the same rate of pull on all objects, but I don't remember.

Any advice is appreciated.

Depends on the round you're shooting, the ballistics and scope height (above bore).

For say a 5.56mm M855 NATO MV of 2970fps a zero of 100 yards 2" scope height will have a 1.7" drop at 170 yards
For say a 7.62mm M80 NATO MV of 2800fps a zero of 100 yards 2" scope height will have a 1.9" drop at 170 yards

from the high/low you can figure out the mils/MOA you need to adjust the scope.

For 5.56mm M855 you'd come up 0.9MOA or 0.3mils
For 7.62mm M80 you'd come up 1MOA at 175 yards, or 0.3mils

If you have a mil-dot or MOA reticle on the crosshair you can just holdover rather than adjust, if you're adjusting remember to re-zero to your zero range before adjusting your elevation for the new range, or get zero-stop turrets.

You can get dope cards calculated at Hornady and a number of other places, just do a search for Ballistics calculator, and I'm sure there's a smartphone app that can tell you the exact MOA/mil to adjust by. Use a Chronograph to get your MV, measure your scope height (center bore to scope center), find or calculate your ballistic coefficient, and plug in the numbers. Be aware that your actual dope may differ from the calculated, at short ranges (under 400 yards) it's probably good enough, at long ranges 1000 yards you'll need to generate your own dope. I'd recommend getting a laser rangefinder too, it makes measuring the distance to target far easier and more accurate.

Depending on what you're zeroing for you might find that the variance is better with a different zero, M855 works nicely with a 50 yard zero (known as 50-200), it's 1.4" high at around 100 yards and 1.4" low at around 250 yards but at around 200 yards it's zero again.

[WhipperSnapper 88]

Thanks for the good advice!

[An Einnseanair]

It depends on gobs of things. Unless you are really good at math and have taken a sniper course, you'll need an online ballistics calculator such as: JBM - Calculations

Pick the "Trajectory" one.

To do it right, at a minimum you need your specific bullet's weight, caliber, and ballistic coefficient (from the manufacturer) and the speed at the muzzle (a direct chronograph is best, or else tables from the manufacturer for a good guess). You also need height of site above the bore. This is for a level shot with no wind. If you are shooting up or down hill into or out of a stiff wind everything changes. You can run the calculations and print out a card that can be taped to your stock for quick field reference.


All this said, unless you are trying to punch out bulleyes, do head-shots on squirrels, or shoot at ranges over 200-300 yards, I recommend reading up on Maximum Point Blank Range (MPBR - ShootersCalculator.com | Point Blank Range Calculator). It's where you figure the maximum vital area for whatever you are shooting at (4" circle for coyotes, 6" for whitetail, etc.). Then you set your sites such that if you aim at the center of the vital area the bullet will stay within that circle out to a set distance and wind speed. For a .223 with a 4" vitals area you can go out to 200-250 yards (depending on muzzle velocity and BC) without having to take the time to calculate trajectory... just aim and shoot.

[M3 Mitch]

Originally Posted by WhipperSnapper 88

I'm sure this will sound like a dumb question, but I'm new to long range carbine shooting.

I have my rifle scope zeroed at 100 yards, so my question is, what if I'm shooting at a target at about 170 yards? How would I know how many clicks I would have to move the elevation up?

I thought I heard some kind of formula for figuring this out before, since gravity has the same rate of pull on all objects, but I don't remember.

Any advice is appreciated.

Depends on the bullet you are shooting and initial velocity. Back in the day, Winchester and Remington catalogs listed nominal drop at 100, 200, etc. out to 500 yards for their factory ammo. These were, I think, slide rule calculations based on claimed muzzle velocity, which tended to be taken in pressure test barrels, which were generally longer (say 26") than typical production rifle barrels, and of course longer than the typical 20" or shorter carbine barrel. Claimed muzzle velocity tended to be a bit optimistic. You didn't want to publish that your ammo gave a lower velocity than your competitor's.

You can get software that will give you drop for handloads, even cast bullet rifle handloads. Look in any gun magazine and you will find the ads.

All this has to be taken with a grain of salt, bullets don't fly straight but rather in a spiral (ever see this?) so the best way to find out drop for a specific range is to fire a few groups.