The barrels on that .577 are quite stout!
What is your regulation load with that rifle?
The chamber walls are mondo thick.
Lots of meat at the muzzles too.

The rib extension seems to be a different piece of material from the rib.
Interesting.
Can we see more detail of the rear sight group and rib too?
Neat rifle.

Cool dovetail bushed striker detail on the smallbore rifle too...

Cheers
Tinker