Whatever the choice of ring/base system, make sure the rifle scope (optical axis) and rifle barrel (bore axis) are aligned as closely as possible. This alignment is critical to get sighted in properly and the scope performing its maximum potential. This can be best thought of as the process of aligning the reticle to where the rifle barrel is pointing. SWAROVSKI OPTIK rifle scopes are delivered with the reticle centered in its Range of Adjustment (ROA). In the vast majority of situations, a rifle scope is mounted, several clicks are made to get zeroed, and you're ready for the range or the field.
Every rifle scope model has a unique Range of Adjustment (ROA). ROA is the limit a reticle can move inside the rifle scope. Generally, lower magnification rifle scopes have more ROA than higher magnification scopes. For example, a SWAROVSKI OPTIK Z6(i) 3-18x50 has a ROA of 65 inches of elevation, 36 inches of windage, at 100 yards. This model presents a rectangular shaped box. When the scope is mounted on the rifle, the rifle barrel should be pointing somewhere within this "rectangular shaped box" or Range of Adjustment, preferably relatively close to the center.
Two mounting problems that can happen and to be aware of:
- If the barrel axis/scope axis is far enough apart, after zeroing, it is possible that the reticle (erector system) can be pushed against the inside of the scope's main tube. The result can be the rifle/scope, as mounted, will produce erratic grouping.
- There may even be severe cases when after a scope is mounted, the rifle barrel is pointing "outside" the Range of Adjustment of that individual scope, so that the reticle can not be aligned with the rifle barrel. There can be many, sometimes difficult to detect reasons for this:
- Windage adjustable bases have been used - scope is pointing too far to the left or right of the bore
- Scope base screw holes not drilled true to the bore axis
- Rifle receiver dimension changed - ring & base makers have not been made aware yet
- Rifle receiver slightly over/under machining tolerance
- When barrel was threaded to receiver, bore not squared to receiver, bore now not in line, even with "trued base" hole screws
- There could be dirt between the base and receiver
- A burr is on the base
- Some rifle manufacturers have identical screw hole spacing and identical size screws, but different base heights - wrong bases and rings were used.
Rings and bases should be tightened to a specific torque measured in inch pounds to ensure proper functioning of the rifle scope. Scope rings and base materials used, such as steel or alloys, as well as individual screw sizes determine the appropriate inch pound specification. Over tightening rings can adversely affect performance, especially the scope's ability to hold zero. These specs are provided by the ring and base manufacturer and should be closely adhered to.
Most non-parallax adjustable scopes are set to be parallax free at 100 meters. Some of these (non-adjustable) models with the BRH/BRX/BR long range reticles are set to be parallax free at 200 meters because maximum parallax error will be less at longer ranges. Because of this 200 meter parallax setting, slightly erratic grouping can occur at 100 yards - this is normal. Longer range grouping will be better. [Note: The Z6(i) 1-6x24 BRT(i), are set to be parallax free at 100 meters].
Steel scope rings are usually shipped with an oily film to prevent rust. Make sure to use a degreasing agent to remove oil or grease from the inside of scope rings before the scope is mounted.
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