This weekend we had a shooter with dime-sized groups in stage four. I noted on one target an apparent shift of PoI by 1/4 inch or so of that dime-sized group on a different target in the stage. A few weeks ago I was discussing the matter of sight alignment and parallax with my brother in law-an old sailor. One of his seal buddies, after returning from the sand box, had the opportunity to buy his combat rifle, which had been returned to the contractor. He showed him the rifle with a small soft marker glued to the stock from his days in combat. The seal said he would always put the corner of his lip on the marker. Here is a small article on parallax and apparent shift in PoI. I am considering the seal's trick for my rifle
https://rifle-scope-guide.com/understanding-parallax-in-rifle-scopes/
PS. The shooter did not have an AO and the scope appeared to be a standard centerfire scope - parallax was probably factory set at 100 yards so the 25 meter range could give significant changes in parallax
For AR's I shoot nose to charging handle to help with this.
I do use a Rav Vin objective aperture cap to force me to hold true center on the scope when I'm really trying to be precise.
With optics in general making sure the outer black circle of the scope is concentric with your scope image and equal width all the way around will help.
For non AR traditional stocked rifles finding some kind of index point helps which I guess could be a soft marker. I usually end up with my cheek nestled against my trigger hand thumb or the stock rise behind the receiver which I use in place of a charging handle index point.
What Lomshek said is the same I practice. Nose to the charging handle.
When I recently purchased a bolt actin in 6.5 creedmoor I noticed a great deal of trouble finding the right position.
I almost gave up on the rifle until i accidentally created a hump on my cheek rest Now i index on the hump.
Quote from: Lomshek on June 17, 2020, 01:32:37 AM
For AR's I shoot nose to charging handle to help with this.
I do use a Rav Vin objective aperture cap to force me to hold true center on the scope when I'm really trying to be precise.
With optics in general making sure the outer black circle of the scope is concentric with your scope image and equal width all the way around will help.
For non AR traditional stocked rifles finding some kind of index point helps which I guess could be a soft marker. I usually end up with my cheek nestled against my trigger hand thumb or the stock rise behind the receiver which I use in place of a charging handle index point.
For a more complete explanation of parallax you can see page 41 of the new KD Manual now listed on TIPS. Previous versions of this manual have been listed for years, at: https://appleseedinfo.org/smf/index.php?topic=41791.msg297146#msg297146.
Quote from: dond on June 17, 2020, 10:43:59 AM
For a more complete explanation of parallax you can see page 41 of the new KD Manual now listed on TIPS. Previous versions of this manual have been listed for years, at: https://appleseedinfo.org/smf/index.php?topic=41791.msg297146#msg297146.
"In the preceding section the focal lengths were defined in terms of an object located at an infinite distance from the objective lens, which we initially called the target. However, objects of interest to a rifleman, the actual targets, are not infinitely far away, and as a result, the images of these targets would be located some distance away from the focal point. And, therefore, if the reticle is located at the lens focal point, this means that the target image and reticle would not be at the same point. Therefore, if the eye is placed along the optical axis of the scope, the image and the reticle will not coincide with one another but will be located at different positions along that optical axis. Therefore, as the eye is moved off that axis, the reticle and the image will move with respect to one another. This is parallax and is analogous to holding up your index fingers at different positions along your line of sight so they are aligned with one another, then moving your head so that the fingers seem to move with respect to one another. This parallax can be eliminated in the scope by an adjustment which either relocates the objective lens or by introducing another lens which accomplishes the same purpose. This adjustment can be located either near the objective lens or by a knob on the side of the scope. The result is that the image will then be located at the position of the reticle, which is located at the objective's focal point, thereby eliminating parallax. Scopes which do not have this adjustment feature are designed to be parallax free at a particular distance. For many centerfire calibers, this distance is 150 yards. For rimfire cartridges, it is typically 50 yards. In spite of all this, however, parallax is not something a rifleman should worry about. With a good scope set to be free of parallax at 150 yards, according to Leupold, the maximum effect of parallax will only be 1.3 inches at 500 yards. And if a good cheek weld is achieved habitually, even this minor effect will be significantly decreased. However, it should be mentioned that for fairly short distances, parallax will become more significant...."
I should have responded to another item in the link provided above in my first post on the subject, but declined at the time. However, I just can't let it pass without comment. Reference is made to looking at an x through a glass of water and moving your eye from above it, and that this is an example of parallax in action. In actuality this observation has absolutely nothing to do with parallax. Instead it is an example of refraction of light. The topic of refraction is also treated in the KD manuals referred to earlier, but in relation to another topic of interest to riflemen.