This is a Warne 20 MOA rail, and Seekins rings holding a Vari-X III with turrets.
The rail is long enough to get the scope somewhat forward of the hammer. A fixed power would be able to go further forward without the power ring.
I only kept the scope onboard for a short time. Wanted to keep it slim/trim, and went to XS ghost ring sights.
Here's a pic of a friend from the UK shooting the irons.