Whenever we get into a discussion with someone about rifle scopes, inevitably the subject of parallax arises. Scope parallax confuses a lot of people, and there is a great deal of misunderstanding on the subject.
First things first; the term parallax is used to describe the difference in angles between objects that are seen up close and those seen far away. When you are driving and look at telephone poles pass by on the side of the road, those closest to your car seem to pass very fast, while the ones far away seem to go
very slow. That difference is due to parallax.
In general, it is wise to keep the old phrase in mind, The better you can see your sights and your target, the more accurately you will shoot. However, that phrase is only true as long as your sights are pointing in the same place from one shot to the next. Telescopic sights allow you to see much further distances, but they create new sighting problems with rifles that never were a problem in the old iron-sighting days.
A scope with parallax issues can wreak havoc on a persons air rifle accuracy as well as sanity! We see this issue frustrate people to no end time and time again in our service and gunsmith departments. If you dont know whats going on and how to check for this problem then you could be wasting hours at the range trying to figure out what is causing the accuracy problem.
Many modern day airgun scopes have an adjustable objective (AO) feature, which is located at the forward end of the scope or the turret. There will be an adjustment ring with yardage numbers that can be rotated to coincide with the distance at which you are shooting.
If you are suspicious that there may be parallax issues with a scope then place the gun in a solid rest that totally supports the gun without you holding it. Place a target at a known distance and set the AO ring to coincide with that particular
distance. Adjust the gun rest so that the crosshairs are centered on the bulls-eye. Now, move your head left and right about 1 in each direction. The crosshairs should remain centered on the bulls-eye as you move your head left and right. If the crosshairs are wandering off the bulls-eye then there is an issue with the parallax at that distance for that scope when you are shooting it.
It should be noted that distances marked on the scope are not necessarily written in stone. A persons own optics of their eye comes in to play for a certain scope at a certain distance. Some scopes do not put markings on the scopes for this very reason, instead saying to use the test (above) to find the point of zero parallax error for each distance and then use a silver or white paint pen to mark the positions. If you do notice an issue with parallax on your gun, you can try rotating the AO incrementally to see if the parallax issue can be eliminated, and then noting the position that the AO is in for that distance. If you are unable to eliminate the parallax, then we suggest replacing the scope with another one.
The parallax issue is a critical one for hunters and target shooters. The crosshair remaining centered on the bulls-eye when moving your head left and right is of utmost importance. The reason beingif you didnt position your cheek at the exact same spot on the stock each time you are shooting then it would be like moving the rear sight, which of course changes your point of impact. By its very nature, parallax is more of an issue at close distances and becomes less of one the further out one aims. Because air rifles are usually aimed at much closer distances than firearms, parallax can be much more of an issue among air rifle shooters.
So, if you find yourself becoming increasingly frustrated with sighting in your rifle, look at parallax as an issue that might need to be eliminated.