Thanks for the replies guys. I thought the shrouded barrel with brass insert could have been someones signature. I think it was probably done by the same person because the shrouded barrel won't fit in a standard stock, and that custom stock has been inletted for a wider barrel.

The serial number is 45379, possibly late 90's? Anyway thanks for checking.

It's definitely got a spring, you can see it through the cocking slot. Not one of those awful square-section ones either!

Cheers
Greg