They look very much like Kozap bases.
Many Thanks Neil
If your L591 has the standard Sako tapered dovetails on them, you can fit a set of Sako Opti-Lok bases and rings, or the QD Opti-Loks, if you want to switch between scope and iron sights.
Leupold makes several rings in various heights and in 1" and 30mm, for the Sako integral dovetails.
Warne used to make them, and in QD, but no more. You may find a set of used ones.
You should also look for the original Sako rings, with the large thumbscrew with a slot to take a coin for turning it tight.
Thanks for the explanation Southern - much appreciated. I've just been looking at the optilock range now.
Thank you for that . I picked some off intending to use them on a project which of course never happened. Always wondered who made them.