Sight Radius
- for pistol, this will be the distance between the highest part of the front sight and the rear of the back sight
- for rifle, this will be the distance between the rear of the front sight insert and the rear surface of the back sight aperture
- sight radius is not really applicable to Running Target or Shotgun
Of course a longer radius usually goes hand in hand with a longer barrel which can increase fatigue and make your arms unsteady too.
Effects of perception
For perceived ratio between blade width and rear sight gap there are three factors to consider:
- Distance from front sight blade to eye
- Distance from rear sight to eye
- Physical width dimensions of the front blade and the rear sight gap
It should be noted that the distance from the shooter's eye to the sight combination (dependent on the shooter's stature and stance) is an important consideration:
- For a shooter who holds the pistol closer to the eye (smaller stature and/or bent arm), the rear sight gap will appear wider in relation to the front sight blade
- For a shooter who holds the pistol closer to the eye, the front sight will appear wider in relation to the target.
Due to the effects of perspective, the rear sight gap will APPEAR wider in relation to the front blade – e.g. for a front sight blade width and rear sight gap both of 3mm, the APPARENT sight ratio for most shooters:
- with a sight radius of 200mm will be around 1.25:1
- with a sight radius of 150mm will be around 1.1:1
Effect of short sight radius
- decreases the apparent effect of pistol misalignment as seen at the sight picture
- decreases the apparent sight ratio
Effect of long sight radius
- increases the apparent effect of pistol misalignment as seen at the sight picture
- increases the apparent sight ratio
Effect of Sight Radius for Rifle
Given that there is little difference between shooters for the eye/rear sight distance, the main perceived difference from sight radius is in the relationship between the front sight and the target.
As a rule of thumb, no matter who made the sights, if your sight radius is typical, movement of the sight 0.006" will move your point of impact one minute of angle.
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