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The first UK .20 of note was the AIRGUNAID SP-5 .20 Hunter circa 1979. This was developed by Eddie Barber of 1970s/1980s Air Gun World fame, alongside a chap called Don Grey, who produced and marketed his own version of the very same -- both using Lothar Walthar barrels, finely fettled Milbro Diana G80 actions, and specific HW35 styled finger grooved stocks.

Early AIRGUNAID stock examples were hand waxed and hand finished. Later variants -- and all the Don Grey derrivatives -- had their stocks mechanically mass laquered for reason of production cost economics. By today's standards, as I have been forced to admit in the past, the AIRGUNAID and DG .20s in question are left wanting in many areas, but I for one love them.

Do a BBS collector's section search for AIRGUNAID and see what comes up -- I think you will be very pleasantly surprised. Hope this helps and offers an insight into the quirkiness of the 1970s/1980s British domestic sub 12ft.lbs air gun scene.