While we are on 80's BSA's then these all shoot really well with their iron sights.

If you must scope them then they really demand nothing bigger than a 3-9x40. A 3-9x32 AO would be very nice. Frankly a 4x40 would hit anything in the farmyard. Annoyingly BSA branded scopes weren't often found and those that were weren't very good. Most the nasty 4x20's that have stamped metal mounts. For the blonds there were some 2-7x20/24/32??? with gold front ring and better glass. Sorry I haven't seen on example for a while, but they were 2-7x???.

Mounts then there is a set back Apel mount. Sportsmatch did them too but are bulkier. BSA scope groves aren't deep and scope creep was rife. Arrester blocks of various forms were about including one that needed drilling into the rear block.

BSA really didn't make life easy for us. Only sorted when the Challenger and Silverstar/Goldstar came out.

A well sorted Mercury is fast to load and hits with a punch. They can be tuned a tad to be smooth and well able to hit anything within the farmyard with a bit of practice and trigger time. Young eyes help with iron sights.