Thermal Scopes, Buying Guides, Troubleshooting
Bristle Up Scope Tools
Check your scope will fit your rifle, and work out your scope height
See how much room the front of your scope has, and which ring heights fit.
Where to measure
- PHPicatinny height
- This is the measurement of the space available between your barrel and the top of the Picatinny rail.Not needed with a full rifle Picatinny.
- ODObjective diameter
- Lens size and the actual objective lens diameter are not the same. You need to take real measurements from the scope.
- RHRing height
- The height listed on Picatinny rings and uni-mounts is commonly measured from the top of the Picatinny rail to the centre of the scope.
Receiver PicatinnyPH + RH − (OD ÷ 2) = clearance from barrel
Example: 13 mm + 28 mm − (69 mm ÷ 2 = 34.5 mm) = 6.5 mm
Full rifle PicatinnyRH − (OD ÷ 2) = clearance from rail
The rail runs under the front of the scope, so the scope has to clear the rail.
Scopes with a ballistics rangefinder ask for your scope height. Three measurements with a set of verniers give you the number.
How to measure
You need a set of verniers. There are three measurements to take.
- 1Measure the housing
- Measure across the outside of the scope’s housing.
- 2Measure the bolt
- Add those two numbers together and divide by two. That finds the centre.
- 3Measure the gap between them
- Measure the distance between the top of the bolt and the bottom of the housing, and add it to that number. That is your scope height.
Scope height is the distance from the centre of the barrel to the centre of the scope. The bolt sits in line with the barrel, so you measure from the bolt.
(Housing + Bolt) ÷ 2 + Gap = scope height
Example: (46 mm + 18 mm) ÷ 2 = 32 mm, then 32 mm + 27 mm = 59 mm