Complex sentence: The gun was a firm favourite among shooters in the 1970s and 1980s, the piston, chamber and barrel are similar to the BSA Meteor Air Rifle but the internal dimensions are different and parts are not interchangeable.
Split into simpler sentences: The gun was a firm favourite among shooters in the 1970s and 1980s. The piston/chamber/barrel set up is similar to the Meteor but the internal dimensions are different and parts are not interchangeable.