Tuesday, September 10, 2013

Sighting-In Optimization with - The Kill Zone Method

Some AR-15 groups at the range.
Ever wonder if there is a range that you could sight-in, or “zero”, your gun that would allow you to just aim-and-shoot and be confident that your shot would do its job? For practical purposes, there is. This is how you can find it and “optimize” your gun sight.

My quest for finding the best sight-in range began with my first scope on my .22 rifle many years ago. Of course I wanted to hit my target at any range but a decision had to be made for that bulls-eye setting. I looked over ballistic charts for the .22 LR. The charts provided rise and fall of a bullet in relation to a line drawn between the muzzle and the target for different range “zeros”, stepping from 25-yards to 100-yards. So the normal thing seemed to be to just pick one of those chart distances for your sight-in zero and memorize the rise and fall figures for the other distances. This information was helpful to know, but it didn’t take into account the height of the sight. Well, call me picky, but that didn’t seem to be the best way to decide what range-zero was best or how to get the most from my gun. Besides, I didn’t want to be doing math while about to make a shot. So I did a little thinking on the matter.

I developed a way to account for my sight’s height above the muzzle and eventually a way to see where my bullet would track with my rifle sighted at any range. It involves making graphs to show the arched trajectory curve in relation to the line-of-sight. With it I could examine the various sight-in ranges to see which one kept my bullet as close to the scope’s sightline as possible for the greatest distance. But I had to decide upon the maximum bullet deviation from the sightline that I felt would still allow a kill-shot if the bullet stuck there instead of dead-center of my sight’s crosshairs.


The Kill Zone:

I envisioned what I call a “kill zone.” Think of shooting down a long, imaginary tube to your target. The tube must be small enough for the bullet shot through it to hit the vital area to kill your target: One shot – one kill. The centerline of the tube is your line-of-sight, which may be represented by crosshairs, red-dot, etc. The tube’s radius represents the allowable bullet deviation that will keep the bullet in that vital area. It can be whatever you decide. For a small-game hunter, the zone radius might be 3/8”, and for a deer hunter it might be 1-1/2” or more. That is equivalent to drawing a bulls-eye on each: ¾” diameter and 3” diameter, respectively. Once a kill zone size is chosen, the sight-in distance can be determined from the trajectory curves. The sight can now be adjusted for optimum use for the combination of gun, sight, ammo, and target involved.



The Easy Way to Optimize Your Sight:

Today it’s not necessary to draw trajectory curves, etc. Now we have personal computers and a smart-phone app for almost anything, including ballistic calculations. I recently discovered the Winchester’s ballistic calculator and iPhone app at their website. These can be very useful for making the right decision for the best range to zero your sights.


Trying it, I noticed some limitations: You are limited to Winchester brand ammo for your selections, and your selection of range. And range interval selections are somewhat restrictive on the phone app. I found that, using the computer-based Winchester “Ballistic Calculator,” a close approximation of your “optimum zero” can be determined. Using the phone app works, too, but due to its limitations and tiny screen, it will only get you in the ballpark of that optimum setting.

Here’s the key: Find the bullet trajectory curve with a bullet rise above sight line that is closest to your kill zone radius. That trajectory curve will become your curve.

In WWII they didn't have computers to help sight-in.
You can bet they wanted a method to hit where they aimed
within a useful range, though.
(That's Jeremy and Jason's grandfather, Almon White, on the left,
practicing with his M1 Carbine in the Philippines, about 1944.)
To find it, I suggest these steps: Using the PC version of the ballistic calculator, select your ammo and set the scope height. For conditions, change the defaults for “range” to maximum. Select the minimum interval for the graph range spacing. Then “shoot” and you will see the curved path of your bullet drawn across the screen. From it you can determine the plus and minus (-) height of it in relation to your line-of sight all along its path. Next change the “sight-in range” and shoot again. Keep changing the sight-in range and shooting at each until you find the sight-in range that gives a peak bullet rise that is closest to your kill zone radius. When you feel you have it, shorten the “range” to get a better view of the curve, leaving the other settings the same. Then tweak the sight-in range, up and down. Again, you are looking to find the bullet’s peak that matches your kill zone’s upper edge.

Once you’ve found your optimum trajectory curve, note the “near zero” and “far zero” where the bullet path crosses the line-of-sight. These are your sight-in distances. Also note the range limits of your kill zone, near and far.  Then change the “range” setting back to one that you consider your maximum shot distance and shoot the curve again. Note the bullet drop on your curve beyond your kill zone. I suggest using even numbers, like every 50 or 100 yards since they are easier to estimate and remember in the field. The actual trajectory (rise and fall) can be seen at different intervals by clicking “View Statistics Chart” after any shot. Once you select your curve, print the chart for reference.

You can try various bullet calibers, types and weights, and compare them on the same trajectory graph. Other useful insights gained by using the ballistic calculator are the abilities to see the differences in where your bullet will strike when you vary the temperature and with various crosswinds. The effects of those variables are clearly demonstrated. The target on the screen shows where the bullet hits at the “range” setting selected (far right end of the curve) and for the conditions you selected. Just hover over the bullet strikes to see the dimensions since the target ring spacing can be deceptively large.

Before going to the shooting range, make sure your scope is mounted securely, with the proper torque applied to the mounting screws. I recommend using blue* thread-lock adhesive on the screw threads to insure they don’t loosen after repeated recoil. I once purchased a rifle with the scope already mounted on it to later find, after a firing a box of cartridges, that the screws had loosed. The day was lost and the entire sight-in process had to be repeated after I re-mounted my scope.  (*The blue variety will allow the glue to snap loose with pressure should you ever need to remove the screws. The red variety, will not.)

When sighting-in your gun, use a good bench-rest for the best results. Adjust the sight for the “near zero”; then, since distance amplifies small errors, fine-tune it for the “far zero.” Your sight is now “optimized” and ready for serious use.

With that optimum zero distance sighted-in for your scope, red-dot, or iron sights, there is no mental calculating to do in the field as long as the quarry is within the kill zone range limits: Just aim and shoot.

Try shooting at varying distances within the limits for your kill zone. Be sure to shoot at the zone limits to help establish those limits in your mind. I also suggest shooting at longer ranges, beyond your kill zone, to help establish the distances and hold-over sight-pictures in your mind’s eye. Hunters will want to envision that hold-over on game.

The ballistic calculator is a shooter’s tool that I recommend. The calculator’s selections may not fit your exact gun or ammo, but the selections offered will get you very close to a great, practical set-up for your rifle or handgun. You can try it at the Winchester website. And, there are other similar programs and apps available. Just search “ballistic calculator.”


For the Long-Range Shooters:
Most of you know that another way to compensate for bullet trajectory is by choosing a riflescope with built-in range compensation. Leupold and others make them. It appears that you should still pre-select a range setting for carry – for that quick shot. So this information should be useful even if you use one of those fancy riflescopes. Plus, using this ballistic calculator, you can see the bullet drift due to crosswinds – something that may be even more helpful than my suggestions. 

For my shooting purposes, I don’t feel the need to spend more on newer, compensating scopes just for that. My scopes are already optimized.


Examples of Optimized Sight Selections:
The following are a few examples of the results I got using the Winchester ballistic calculator for various guns with kill zones and bullets that I selected. You may find them useful.

Remember, the “kill zone radius” is half the diameter of an imaginary bulls-eye on your target. In addition, your gun’s sight height may be different from the height I used.

Barrel lengths are set in the calculator and cannot be changed. However, some pistol bullet selections were tested from different length barrels so you may find what you need by trying various bullets.

Note: Some Bullet Drop numbers are rounded to the nearest half inch. All figures are estimates based on data obtained from the Winchester Ballistics Calculator. Your actual results may vary slightly.

The blue blocks are the points for near and far zero with each load.

Hunting Rifles:



.22 WMR – Scope 1.5” above bore; 40gr. JHP; 3/8” Kill Zone Radius
Optimized Kill Zone Range: 20-85 yards
Range (yards)
10
35
70
100
150
200
Bullet Drop
1”
0”
0”
1.5”
8.2”
21.5”



.44 Mag (rifle) – Scope 1.5” above bore; 240gr. HSP; 1.5” Kill Zone Radius
Optimized Kill Zone Range: 0-85 yards
Range (yards)
10
18
75
100
125
150
Bullet Drop
1”
0”
0”
3”
9”
16”


Hunting Handgun:



.44 Mag (handgun) – open sights 0.9” above bore; 240gr. HSP; 1” Kill Zone Radius
Optimized Kill Zone Range (for 4” barrel): 0-70 yards
Range (yards)
10
12
60
80
100
-
Bullet Drop
0.5”
0”
0”
2”
5.5”
-


The 9mm Pistol:



9mm Pistol – open sights 0.5” above bore; 0.5” Kill Zone Radius
For both 115gr JHP and +P 124gr PDX1 Defender
Optimized Kill Zone Range (for 4” barrel): 0-50 yards
Range (yards)
Muzzle
5
10
40
50
-
Bullet Drop
0.5”
0.25”
0”
0”
0.5”
-


Comparing Ammo for a .45 Model 1911 Pistol:



.45 ACP (1911) – open sights 0.6” above bore; 0.6” Kill Zone Radius
230gr. FMJ
Optimized Kill Zone Range (for 5” barrel): 0-42 yards
Range (yards)
Muzzle
7
35
50
-
-
Bullet Drop
0.6”
0”
0”
1.5”
-
-


.45 ACP (1911) – open sights 0.6” above bore; 0.6” Kill Zone Radius
230gr. PDX1 Defender
Optimized Kill Zone Range (for 5” barrel): 0-43 yards
Range (yards)
Muzzle
8
35
50
-
-
Bullet Drop
0.6”
0”
0”
1.25”
-
-

.45 ACP (1911) – open sights 0.6” above bore; 0.6” Kill Zone Radius
185gr. Silvertip HP
Optimized Kill Zone Range (for 5” barrel): 0-45 yards
Range (yards)
Muzzle
10
35
50
-
-
Bullet Drop
0.6”
0”
0”
1”
-
-


The AR-15:


.223 Rem – Scope 2.7” above bore; 55gr. FMJ; 1.1” Kill Zone Radius
(For 1:9” twist rifled barrels)
Optimized Kill Zone Range: 40-225 yards
Range (yards)
10
25
73
200
300
400
Bullet Drop
2”
1.5”
0”
0”
6”
20”
 



4 comments:

  1. You went all out for this article Dave! Good work!

    ReplyDelete
  2. I’ve lately began a blog, the data you provide on this site has helped me tremendously. Thank you for your whole time & work.

    ReplyDelete
  3. This comment has been removed by the author.

    ReplyDelete

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