Hi David, a wide topic area this. There have been absolutely hundreds of variants of the underlever air rifle made with loading taps since 1901, and they came from many manufacturers, all of whome in turn produced many different models along the same theme... The main manufacturers however were Lincoln Jefferies, BSA, Haenal, Diana, and after WWII Webley & Scott with their MkIII. BSA also produced a sliding rotary breech underlever in the early 1900s and redesigned it for an Airsporter variant and range of rifles called Superstars in the 1990s (this re-vamped rotary breech being known as the second type RB-2), and HW and AA produce sliding breech loading underlevers such as the HW77, HW97, TX and Pro-Sport to this day (a bit vague but hope this helps ). Atb: Gareth W-B.