Calculating scope to rifle body clearance
The way you calculate the clearance is by halving the overall OUTSIDE diameter of your rifle scopes objective lens and then deducting half the rifle scopes body tube diameter.
For scopes with a 1 inch diameter body tube this means deducting 12.5mm.
Note we say OUTSIDE diameter - this means NOT the lens diameter, you need to measure the whole outer casing diameter.
The result gives you the minimum "saddle" dimension required - the measure from base of mount to bottom of the ring - the 'A' dimension that is shown above.
The amount the saddle dimension is greater than the figure you have calculated is the amount of clearance your scopes objective will be clear of your rifles body. The saddle on these mounts is -
Worked Example -
- A scope has an outer case measurement of 51mm.
- 51 divided by 2 = 25.5.
- 29 minus 12.5 = 12.8mm
- So the mount must have a saddle measure (base of mount to bottom of the ring) greater than 12.8mm or else it will ground out on the rifle body.
Keep in mind that flip up lens caps may add 2mm or so.
Calculating your rifle scopes clearance assumes that:
- Your dovetail or base is not raised above or below your rifles barrel
- Some rifles with grooved receivers such as some models of airgun and .22 rimfire will mean the scope sits lower
- A raised dovetail base or Weaver/Picatinny base may add height
Note some rifles with high or adjustable cheek pieces may require higher scope mounts or risers so that your eye is in line with the rifle scope and your head is kept in an upright comfortable position.