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Thread: Scopes - How to Zero a Scope
01-13-2009, 04:06 AM #1
Scopes - How to Zero a Scope
We are using a Remington 700 5R in .308 Win with a Leupold 1/4" MOA VX-III scope in this article as an example. We are setting a zero at 100 yards that will be sufficient for up to 200 yards.
Step 0 - Quick Run Down
The top adjustment knob is the elevation adjustment. The knob on the right is the windage adjustment. Windage is the right / left adjustment. Your scope might have an adjustment knob on the left or forward on the objective bell with a bunch of different numbers (0 to infinity for example). This is the parallax adjustment. Go ahead and set this to 100 yards.
One thing to always remember is Right - Down / Right - Left. Meaning if you turn the scope knob clockwise (to the right) you will move the shot down using the elevation knob, or left using the windage knob. You can verify this by looking on your scope.
Look at your scope before you start. Is it tight? Is it mounted right?
Check your ammo. Is it the right caliber (you'd be surprised), is it what I am going to be always using for this zero? A change in ammo style, down to the brass, primer, powder charge, powder make, etc. will affect it's shot placement and cause you to have to re-zero the rifle.
Step 1 - Setting the Rifle Up
You should invest in a set of bags. I own a cheap set from Caldwell that get the job done. You simply cannot zero the rifle without having a repeatable environment, and the foundation of that is the rest that the rifle sits in.
My M1A in my Caldwell Bags
When you place the rifle on top of the rests you should ensure that the front rest is under a bedded portion of the rifle. Failure to do so will cause the stock to be pressed into the barrel causing a completely different harmonic profile and the resulting inaccuracy. The best position is right under the breech / chamber portion of the gun.
Step 2 - Gross Adjustment
If you've bore sighted the scope then you can skip the next paragraph.
Setup the target at 25 yards, and center the scope on the target using the front and rear bags. Remove the bolt and peer through the barrel. If you see the target through the barrel then you are ready. If not, move the gun onto the target and adjust the scope accordingly. If you are off by a good amount then you need to remount the scope. See this thread for proper scope mounting: http://www.texasguntalk.com/forums/s...ope-setup.html
Choose a target that has 1" squares on it so that you have a visual reference of shot placement, and how much you need to adjust over. It helps to have two so you have one for reference at the firing line.
Load the gun and fire your first shot.
Let's assume the first shot hit 3" low and 3" to the left and felt like a clean shot. Since the scope is 1/4" MOA and we are at 25 yards each click will adjust 1/16". I'm going to explain MOA since alot of people have trouble with this at work.
Using a 1/4" MOA Scope each Click will Adjust:
1/16" at 25 Yards
1/8" at 50 Yards
1/4" at 100 Yards
1/2" at 200 Yards
3/4" at 300 Yards
1" at 400 Yards
2.5" at 1000 Yards
As a comparison a 1 MOA Scope will move:
1/4" at 25 Yards
1/2" at 50 Yards
1" at 100 Yards
2" at 200 Yards
10" at 1000 Yards
Since we are at 25 yards, and we hit 3" to the left I am going to need to adjust the scope to the right.
3 x 16 (Clicks to an Inch) = 48 Clicks
I dial in 48 clicks turning the windage knob counterclockwise.
Leupold Adjustment Knob - Marked 1/4" MOA
The goal at 25 yards is to be within 1" of the bullseye on the windage, and at, or below, the bullseye. You do not want to be above the bullseye. This is because the bullet will rise between 25 and 100 yards. For more info on that see this thread:
Once you have the adjustment dialed in, fire your second shot. Verify that it is centered in the target, and roughly the same elevation.
Step 2 - Finite Adjustment
At this point we are going to run the target out to 100 yards. During this interlude we want to make sure the barrel is remaining cool. You do not want it warmer than luke warm. If it is warm to the touch, let it sit for a solid 2 - 3 minutes before you start the finite adjustments.
Load the magazine all the way; in this case 3 rounds. You want to do this because you don't want to come off the rifle or move your head between shots. With some long-action rifles like .30-06 for example you may have to slightly lift your head or twist away to avoid the bolt. Ours in the article is a short action.
Fire the first shot, you should be somewhat in the ball park and have a small adjustment in windage and a few inches in elevation. Without moving, reach over and adjust the knobs the proper amount. This is where a click type scope is far superior to a friction type.
Cycle the action without lifting your cheek off the gun and fire the second shot. At this point you should be dead on, or needing a small adjustment.
We want the rifle to be 1.25" - 1.5" high at 100 yards for this particular load. This allows us to be within a narrow shot window for ranges between 100 yards and 200 yards. Check your ammo box for a drop chart to reference shot placement.
Step 3 - Diagnosis
If you are having to take more than about 5 shots, or your shots seem to be eradic then you need to do the following:
- Check the scope mounts. Are they tight?
- Check the scope for marks on the tube. Is it moving?
- Check the ammo. Is it the proper load for the gun?
- Check the barrel. Is it cool, or is it ready to cook breakfast?
Guns with bull barrels and relatively slow rounds will stay cool through a string of shots fired in slow cadence. Guns with standard or narrow tapers, fast rounds (.204 Ruger, 6mm Rem Ack. Improved, etc.), and in high ambient temp environments will heat up in a pair of shots.
If the gun shoots bad no matter what you change, including the shooter, then I'd look to the crown or barrel being the culprit.