by B.B. Pelletier
I hope to dispel some of the myths about scopes today. If you saw the movie Quigley Down Under, you saw a mythological gun that could hit its mark at fantastic distances, even when held offhand. In the first demonstration, Matthew Quigley just attached the tang sight after a 3-month ocean voyage and adjusted it after estimating the range to an oak water bucket at least a quarter-mile away. He then proceeded to hit the bucket three times from the offhand position. Pure Hollywood - fun to watch but never happens in real life. And so it is with scopes.
Optics tend to shift
The metallic tang sight Quigley used is actually able to maintain a zero far better than an optical sight such as a riflescope. Optics tend to shift as the temperature changes, and points of impact do the same. For an optical sight to work properly, it either has to be re-zeroed or the zero must be confirmed all the time. Snipers know this and have ways of compensating for temperature shift, but the average shooter knows nothing of this phenomenon. He is surprised and feels cheated when his zero moves by a half-inch at 50 yards.
I'm not talking about a sudden jump of one inch or more in the point of impact. That's not caused by this situation. I'm talking about the gun that was zeroed on a 70-degree day and now shoots a half inch low on a 35-degree day. That shift is due to the change in temperature. But that wasn't the question - was it?
No - the question was how repeatable a scope's adjustments are. I just thought some of you might like to know about the fallibility of optical sights, so you wouldn't fall into Hollywood's deception that a bullet always goes to the intersection of the crosshairs! Repeatability refers to the adjustment knobs. When you make adjustments, will they come back to the same spot if the knobs are turned back to the same settings? That's repeatability!
No doubt, you're aware that scope knobs are supposed to move the impact of the round by a certain distance at 100 yards. The most common distance is a quarter-inch, so we call these adjustments quarter-minute clicks. Since a minute of angle is so close to one inch at 100 yards, it is customary to think in terms of inches: one click equals 1/4" at 100 yards. Nice thought, but not entirely accurate. Some quarter-minute scopes actually move the round a fifth of an inch, while others move it a different amount. The click values are approximations rather than precise values. However, EACH click should move the round by the SAME AMOUNT in a quality scope.
Also, some scopes need to have a shot fired after adjustment before they move to the new point of impact and settle down. Some go there immediately, but a lot do not. I am not sure what this is caused by, but you should know about it. Please do not ask me which scopes do this and which do not - I don't know! I only discover it when testing a certain scope.
Now, we've come to the heart of the question. If you move a scope's adjustments and them bring them back to where you started, will the rounds be striking in the same place? I know you want a black-and-white answer...and there is one...but you have to make certain allowances. The first being this: Can YOU put every round through the same hole with the rifle you are testing? You shouldn't test scope repeatability at close range. Test it at least at 30 yards or more, so you can really see the separation of the shots. If you're shooting a rifle that can't group better than 2" at that range, how will you ever know what the scope is doing?
Yes - a good scope is repeatable!
With a quality scope, it's possible to adjust the knobs and bring the shot group back to the original setting - PROVIDING THAT:
1. The temperature doesn't change dramatically AND
2. The adjustments are in the middle of the scope's adjustment range AND
3. The first shot after adjustment can be discounted, if necessary.
The way to demonstrate this is to shoot at a target at least 30 yards away. Start with the scope sighted to strike somewhere away from the aim point. Shoot a five-shot group, then click 20 clicks of elevation and shoot a second group. Then 20 clicks to the right (or left) and another group. Then 20 clicks down and another group. Finally 20 clicks to the left (or right) to come back to the original group. If the last five shots fall on top of the first five, you have demonstrated repeatability.
To see what this looks like, read Test Two in Tom Gaylord's article They asked for it!