Quote Originally Posted by ogilkes View Post
When did the Airsporter MK1lose it's adjustable sight and gain the flip up.
Quote Originally Posted by mallyally View Post
when it got a scope rail and became the mk2 I think !
Not claiming great expertise, but I believe the really serious BSA researchers have identified various transitional examples that combine features of the Mk1 and early Mk2. IIRC, the Mk2 differed in the stock, barrel profile, machining of the front end of the cylinder, scope mount cuts, and rear sight, and probably other points of detail, so plenty of opportunities for transitional hybrids to have been made.

But, yes, basically the folding sight is supposed to be a Mk2 feature, along with the scope mount cuts (later grooves).