Carl,

The FWB6xx used 22 mm foresight elements.

In my many years, I have never seen metallic 22mm inserts - only plastic or variable iris'.

Please have a peek here :

https://www.intershoot.co.uk/acatalo..._Elements.html

https://www./str/olympicmarksmanequipment

Have fun & a good Bank Holiday

Best regards

Russ