Home Forums Hunting & Shooting Ask The Gunwriters Paralax Error & Raised Cheek Rest

Your body would also need to be in the exact same position because it supports your head.

You can actually calculate the maximum error attributable to parallax, and it may well be rather less than you think at the distances we're talking about:

The maximum parallax error E at a given target distance t for a scope which is parallax-free at distance p and has an objective lens diameter D is given by the equation

E = 0.5 D (abs(t-p))/p

So, for example, if you have a scope with a 40 mm objective lens, like the Leupold KC mentioned, set to be parallax free at 150 yards, maximum parallax error at 200 yards is

E= 0.5x40 (abs(200-150))/150

=6 2/3 mm

Similarly, for a target at 100

E= 0.5x40 (abs(100-150))/150

=6 2/3 mm

That is to say, if your eye position is at the very edge of the exit pupil, rather than properly centred, you could be as much as 6 2/3 mm (roughly 1/4") off at these distances, in these particular examples.

The parallax isn't always correct for the distance it's supposed to be set for. Even with adjustable parallax scopes the distance setting isn't accurate. Of the half dozen scopes I own with parallax adjustment only one has settings that actually match the distance - it's a Bushnell BTW

It is ugly but you could make a temporary raised cheek piece and see if it helps before buying.

I used a 2 inch diameter closed cell foam pipe insulating tube, box cutter, tape and veterinary self adhering wrap. As a harder shell over the foam I placed a piece of Dollar Store plastic cutting board cut and shaped to fit, and taped in place. It was UGLY but helped my offhand/ field accuracy a lot. Once I knew what it needed... I sold the whole rig and started over.

mauserand9mm,

"The parallax isn't always correct for the distance it's supposed to be set for. Even with adjustable parallax scopes the distance setting isn't accurate."

That's pretty common knowledge among experienced shooters--and it's due partly to the variations in manufacturing, and also to variable magnification scopes. It's also less well-known that parallax can vary from day to day, due to air density.

Which is why for the absolute minimum aiming error due to parallax, you have to compensate, which can be done in several ways:

1) Centering your eye behind the scope. This is what KC is trying to accomplish, but its most precisely done by moving your aiming eye closer or farther from the scope than the distance allowing the full field-of-view. This results in part of the FOV being blacked out, which is due to seeing only through the exit pupil. If you center this smaller FOV, and also the reticle, when aiming, there is no parallax, because your eye is aligned with the center of the scope.

2) Adjusting the parallax of the scope. This is easily done with either an adjustable objective lens (AO), or more commonly these days, a knob located on the left side of the scope.

3) Focusing the scope. Parallax can be affected both by the focus on the front of or side of the scope, but also from the two typical adjustments of the rear focus, either screwing the entire bell in or out, or (on many more recent scopes) the "quick-focus" ring on back of the rear bell. This typically doesn't affect parallax as much as 1 & 2, but can definitely help.

4) Variable scopes complicate things, because the change in magnification often results in changes in parallax, which are exaggerated in higher-X scopes. From about 10x down, this isn't much--but above 10x can be--which is why most scopes over 10x feature some sort of parallax adjustment. (In a worst-case example, I once tested a 5-15x scope made by a major "alpha" Eurupean company--which did NOT have any parallax adjustment. On 15x it had around a foot of parallax at 400 yards. I doubt many shooters have seen one, since it did not last long.)

Most scopes up to 10x (including variables) are set at the factory to be parallax-free at a certain range. If they do not have an AO or side-focus, the typical range they're set for is 100-200 yards. If they show considerable parallax at those ranges, then the parallax setting was off at the factory, which is not unknown--which is exactly why I asked AC what kind of scope was the problem.

The model he has should NOT show significant parallax at the ranges he's shooting.

I’ve put Picatinny rails on my las couple of Tikkas and had to raise the comb. I used something like this. Easy to install and addressed all issues without permanent alteration. It did tighten up my groups.

https://www.amazon.com/Beartooth-Co...0G9W1P98&refRID=VQYYW6C3NGRF0G9W1P98

That would be a stupid thing to do.

Gee whiz!

No, it's not a stupid thing to do if you're wondering whether parallax is affecting groups at any range. It's a way of testing scopes (and rifles) that can reveal a lot.

I was not going to comment further but will say that IMO it is a good idea. It is new to me and a scope test I will remember. I would not have thought of it but as soon as articulated, it is obviously true that when the only thing left is the center then you are centered. That is over simplifying what MD posted but is the direction of the exercise: quick, simple and useful.

It was mentioned as a means to compensate for parallax error, and that would be stupid.

You can look through a scope at the correct amount of eye relief and move your head a little to detect parallax error.

I think you can guarantee that any parallax error will affect accuracy at some point.

I don't understand why you would want to waste ammo determining something you can pick up easily just looking through the scope. By shooting you are compounding rifle accuracy (error) with parallax error.

Actually the opposite is true. By pulling your head back and centring the image within the black circle as John describes you eliminate the effect of parallax, so that rather than compounding the rifle accuracy with parallax you can isolate the rifle's inherent accuracy from the effect of parallax. IOW if your groups shrink when you do it, parallax may have been your problem. If your groups are unaffected, it likely wasn't.

I've done it myself. It is quick and simple and is one of those things that can help nail down the source of an accuracy issue. It also may help to shoot the smallest groups with a non-AO scope.

Dan,

"It also may help to shoot the smallest groups with a non-AO scope."

Which is exactly why I have sometimes used it. The last was a few months ago, when assigned by a magazine to test a new bolt-action .22 rimfire hunting rifle for an review article. Despite owning several dozen scopes, a lot of them were already on rifles--including two of the several "test scopes" I keep for such use, which were adjustable for parallax. (As a general rule, there are around 3-4 such test rifles in the safe at the same time.) So I mounted a Swarovski Z3 3-9x36, and shot the .22 extensively at 50 yards with several kinds of ammo, from hunting hollow-points to match stuff, backing off my eye so the reticle could be centered. As it turned out, the rifle would shoot 5-shot groups of half an inch or less with just about any of the ammo, so I decided to buy it from the manufacturer--and then purchased a parallax-adjustable scope to put on the rifle, returning the Swarovski to its usual job of testing centerfires.

On another occasion I was sent a custom centerfire rifle for review, which came from the maker as a package deal with a fixed 10x that turned out to have apparently been set at the factory to parallax-free at 200 yards. It would have been easy to do the testing at 200, but the magazine that assigned the article uses a specific testing protocol that, among other things, stipulates 100-yard group shooting. So I backed off my aiming eye when shooting the test targets, and the rifle shot fine.

I have also come to the conclusion that I can get my face Close to the same place each time using a stock with a higher comb.I am shooting more consistent then I had been in the past since I have changed from a straight classic stock to some form of Monte Carlo.Do I get my head in the exact same spot every time. Probably not,but close enough for me.I really like the McMillan Sako Monte Carlo style stock and have them on several rifles now.JMHO,Huntz

Okay, as a temporary means to get around parallax error is understandable. I thought it was proposed as a permanent fix which would be stupid.

I guess I should clarify my position - sacrificing FOV to correct parallel error would be stupid and potentially dangerous in a field condition. You gotta be aware of the surroundings and background of the intended target. You wanna see that other deer about to cross in front of your intended target, or who knows a farmer or hiker breaking out of the brush - [bleep] happens.

Consider and assess the possiblities of your actions

I use adjustable comb risers

Bolt on one


Strap on butt bag with foam pad,


Shell holder with pads cut from old neoprene waders
[/quote]


I don't use them for parallax error but so when the butt hits my shoulder the scope is in line with my eye and I don't have to be waggling my head around to find the image. The butt bags with pads are as cheap as $8. on amazon and work just as well as the more expensive ones from the LR houses.

I can recommend the beartooth adjustable comb kit. I have two or three of them, I use them on some of my shotguns.... your eye is the rear sight.

I tried one of those and hated it. As with any wrap-around pad, it also makes the comb wider which can push your head off to one side rather than just raising it. It also was not very consistent and stable, as the layers of pad stuffed inside the neoprene sock could shift around. I would not buy another.

There are several kydex adjustable cheek pieces available on Amazon and elsewhere as a kit. You do have to drill holes in the stock though, like erich's first picture above.

Some folks just don't get it when they are told a correct way to test or even shoot. For those folks I dont' think parallax is a big enough issue, they have other issues....

Is it an Oz thing to call someone stupid and then fail to apologize when you realize you were wrong?
Just wondering as I might go to Oz someday.

KC,
As someone previously suggested get a piece of foam pipe insulation, or a pool noodle (if you need more height) and tape it in place. Cheap, easy, and it will tell you what you need to know. Then follow up with a permanent solution if required.