I thought I'd start a separate thread on this topic.
As I continue to evolve as a precision shooter, I am always learning new things. Man, you can really get deep into this discipline! But, that's what I like about it. It's very technical. It's scientific. It's applied Physics. And, of course... the human element. So, as much as I can apply the science, there's always going to be the "art" of it, too. Fun!
So... our scopes come from the manufacturer with a number of different "specs." One of those specs is the turret click value. Most scopes designed for precision shooting have turret clicks that are 1/4-MOA or 1/10-MIL. I'm an "MOA guy," for now. So, according to the manufacturer of my scope, each click of the turret is 1/4 or 0.25-MOA.
BUT IS IT REALLY???
According to what I've read, many scopes are not EXACTLY calibrated to the value in the specs. They can be off a bit. At close distances, it may not matter. For hunting at normal distances, it is probably "close enough" to get in the "vital zone." But, for precision target shooting, it can matter. At longer distances, it can matter even more.
There are various tests you can run to see if your scope is "tracking" well. One of them is the "Tall Target Test." The purpose of this test is to determine the ACTUAL turret click value of your scope. Then, when you are using a ballistic calculator to spit out a "firing solution" at a distance beyond your zero, you will get a more precise result. Make sense?
Here's a link that explains the Tall Target Test process.
So, I went out to the 100 yard range today with the mission of determining my scopes true click value.
Basically, you just need a vertical line down the middle of a tall piece of paper. It needs to be perfectly vertical when it's stapled to the target backer. I used a plumb line to verify. Naturally, your scope needs to be level with your rifle. And, when you're shooting this test, you need to be sure that your rifle / scope is vertical.
After you've confirmed your zero.... Pick a spot near the bottom of the vertical line as your "bullseye." Shoot a group there. Then dial 20 or 30 MOA (or MIL equivalent) UP in elevation. How much... depends on how much room you have to dial up. But, the more the better. In my case, 20 MOA worked well. The first time I did it, I dialed up 16 MOA.
The "Tall Target Test" yielded some very interesting results. I ran the test twice. Both times, the result was EXACTLY the same... to three decimal places! Here are my calculations.
As you can see, my Expected Point of Impact Shift (EPOIS) with 20-MOA (80 clicks) dialed would be 20.94 inches (20 MOA x 100 yards x 0.01047). But, the ACTUAL Point of Impact Shift was 19.688 inches. It was short.
The Correction Factor is what I would use if I didn't have a ballistics app that allowed me to input the actual click value. So, if a ballistics chart (that assumes true 1/4-MOA click value) told me I need to dial UP by 16 clicks (or 4-MOA) for a particular distance, I would multiply that by 1.0636 (about 6%), which would be 17 clicks of actual dialing. If the chart told me I need to dial 40 clicks (10-MOA), that would be 43 clicks of actual dialing.
But, since Strelok Pro allows me to enter in a corrected click value, and my scope's actual click value is short by 6% (6.36%, to be precise), I can just do the reciprocal of 1.0636, which is 0.235. My scope's actual elevation click value is 0.235-MOA. Done another way... 94% of 0.25 is 0.235. I hope that made sense. <img src="https://www.floridaconcealedcarry.com/Forum/images/smilies/smile.png" border="0" alt="" title="Smile" class="inlineimg" />
Consider that at 600 yards, a 0.235-MOA discrepancy comes to 1-1/2 inches.... or half the diameter of the F-class target x-ring (3-inches). So, uncorrected, if I'm holding at the dead-center of the x-ring, the shot would be just off at the bottom... in the 10 ring.
At 1,000 yards, it's a 2-1/2 inch discrepancy.
So, not a HUGE difference, if I'm hunting or ringing steel. But, in a match... could make a difference, eh?
So, the cool thing about Strelok Pro (ballistic app) is that I can enter that 0.235-MOA click value into my scope's data. Now, the app will give me more precise "firing solutions."