Before the Mk1 Airsporter, there was the .177 cal BSA Club
The Aisporter was developed from that and the action is about 15mm longer giving a greater swept volume and more power
The .177 MK 1 Airsporters were called the Airsporter Club and although they are desirable, the shorter/earlier Club is worth a bit more
The MK1 was the best but does not have scope rails
The Mk2 looks very similar but cost cutting resulted in a slightly poorer rifle.
Gone was the tapered barrel which was replaced by a barrel brazed into the breech block. Even the piston was manufactured with cost savings in mind.
Still a lovely rifle though. Although the scope dovetails are shallow and wide apart so mounts are not too easy to source but can be bought
Everything went downhill after that, although the much later standard RB2 models were accurate.
The Airsporter trigger never really evolved despite the number of facelifts which was disappointing.
The RB2 Stutzen is probably the most attractive Airsporter but accuracy was poor. I had one and loved the looks and handling.