I can vouch for the BSA it a reasonable scope. My son uses one and does very well with it .
Barry Taylor does an adaptor for a the side wheel and supplies the shark Finn style. The gaps from 40 to 55 are larger on his than on my big nikko and you can also get a top turret to fit that is for the mk 1 nikko to make the makings better. You will need to remove the existing top turret and the small O ring.
There will be some photos on tomorrow under unofficial manufacturers ( AIR ARMS ) warren Edwards stock if this helps. Don't get a copy one buy a proper BSA from a reputable gun shop.
The range consistent but don't compare to more bigger mag scopes on the market ie big nikko ect.
Over all its nice and light and will do a decent job for you. We payed £119.00 from penningtons
Gun shop in castleford, West Yorkshire .