Parallax adjustment on the objective bell

VIDEO

Traditionally, rifle scopes had a fixed parallax set at 100 meters or 100 yards; however, with the advance of shooting sports, such approach was not adequate anymore. Scopes with fixed parallax offered best resolution only at one distance (100 meters/yards) at which the target was in focus. At all other distances, the picture was less sharp or even blurry. An even bigger problem with this type of scope was the fact that, when shooting at the target not at the same distance as the scope parallax setting, the shooter had to be very careful about his eye alignment with the optical axis. If the eye is moved away from the optical axis, the reticle on the target will move, which will worsen the accuracy. Since these errors are small, the fixed parallax option is still considered accurate enough for traditional hunting. For sports shooting, though, such small error leads to poor results. Parallax errors become more pronounced with magnifications higher than 12x, and that means the majority of scopes with magnification range under this value need no parallax adjustment.

With the ability of parallax adjustment, accuracy of the riflescope is greatly enhanced at all distances. The shooter, however, has to adjust the parallax setting before making the first shot. Such scopes usually have AO – Adjustable Objective or SF – Side focus acronym in their name.

With AO – Adjustable Objective scopes parallax is adjusted with a rotation of the ring on the objective bell; adjusting the parallax this way can hardly be done when in prone position and is not the best solution for situations when parallax must be adjusted often. Due to this reason, such scopes are usually used for benchrest competitions and similar, where parallax is adjusted only initially.

Scopes, which offer parallax adjustment on objective bell, are usually smaller and lighter than counterparts with parallax adjustment on the side focus. They are also cheaper to make and offer adjustment that is more precise. Due to the size of internal mechanism for side focus adjustment, the majority of scopes with tube diameter of 1 inch have an adjustable objective and not the side focus.

The easiest way to correctly set the parallax is to look at the target and gently rotate the ring on the objective. When the target is in focus and the image offers the best sharpness, move the eye from the optical axis in any direction. If the rifle is properly supported and fixed, the reticle should not move on the target when the eye is moved from the optical axis. If it does, parallax adjustment must be fine-tuned until the reticle is still, even if the eye of the shooter is moving around the optical axis.

Do not mind the meters or yards written on the adjustable objective, since they only provide an approximate value. There is nothing unusual if these values do not correspond well with the actual target distances.

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Definition

Benchrest is a shooting sport where the competitor, seated, shoots from a rest with the rifle positioned on a bench or a table.
It takes place at a shooting range, where rifles are placed in the front and rear rest, hence the name 'bench - rest'.
In this sport, one has to be extremely accurate and precise since the targets are very small.
There are two main types: Full-bore and benchrest 50 (BR50).

Full-Bore

In full-bore, competitors use heavy rifles and riflescopes, whereas in BR50 a weight limit is specified. In BR50, small-caliber rifles (.22 LR) are paired with lightweight riflescopes, commonly with a tube that measures 1 inch (25.4 mm) in diameter.

Light riflescopes

Weaver T36 had been the most popular bench - rest riflescope before the introduction of Sightron SII 36x42 BRD.
The latter has gradually stolen the spotlight of the legendary Weaver riflescope which has been in production for more than 25 years.
These light riflescopes are equipped with a tube that measures 1 inch (25.4 mm) in diameter.
The parallax adjustment is located on the objective (AO – adjustable objective).

AO (adjustable objective) parallax adjustment

Since benchrest competitors shoot at a known distance, the parallax is only set once, at the very beginning of the competition. The difficulty to reach the adjustment ring while in the shooting position is thus an unimportant factor. Having the parallax setting on the objective is handy because it allows the user to set the parallax more precisely (the larger the knob, the more precise the adjustments). Furthermore, manufacturing an adjustable objective is less complex than manufacturing a riflescope with a side focus, which is why AO riflescopes are usually cheaper. It also requires fewer parts, resulting in a lower mass.

Benchrest Riflescope Adjustable Objective - Burris riflescope

Fixed power

When it comes to fixed power riflescopes, Sightron and Weaver are the most popular choices. Other well-known manufacturers of such riflescopes are Leupold, March, and IOR. These riflescopes often feature a 1-inch (25.4mm) tube but a 30mm tube is also used by some manufacturers. Fixed power riflescopes are advantageous over variable magnification riflescopes in certain aspects; they are lighter and optically better for the price.

Fully-featured F-class riflescopes

In benchrest disciplines where mass is not to be considered, shooters opt for a heavier riflescope, usually with a tube diameter of 34 mm and a high maximum magnification. A 10–50x magnification range is a common choice, as well as a thin reticle, and 1/8 MOA clicks for maximum precision. Sightron has the most of the market's share in this category, but certain Kahles, Nikko Stirling, and Hawke riflescopes are also popular.

Vortex riflescope SCR-1 reticle - rifle

Vortex SCR-1 reticle

The most popular riflescopes

BR50

Weaver T46
Sightron SII 36x42 BRD
Sightron SIIISS Competition 45x45 ED
IOR 36x42 Competition (legendary status in the EU)

Full-bore

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Parallax adjustment on the objective bell

VIDEO