Re the decline of the gun industry in the UK, post-WWI: I remember discussing the subject with a British gunsmith. He suggested that losing so many of the sons of the shooting classes likely resulted in a glut of second-hand guns appearing on the market after the war. It also explains the effort by makers such as Churchill (the XXV) and those that made the 2" 12ga to offer something new to compete with all the more "traditional" guns that were available after the war.