Lancaster-

Great find!!
Thanks for putting this up.

I question their language of '.577 Express'
Without a chamber cast I really wonder just what kind of charge this rifle was made to handle.
It definitely appears to be a nice looking rifle.
I'd love to see the rest if it.

On date of manufacture, I'd say possibly '63 but much later than that...
This makes me want to see more.

Maybe I can contact the auction house and get more photos and/or more detail.

Cheers
Tinker