Problem
Anyone who has worked "the gun counter" has had the pleasure of listening to customers repeat misinformation they have read about on the web. Although the salesman or service professional must decide for him or herself when to correct that customer, this text is an exercise in relating correct information to the public.
Summarizing the history of the AR-10 and the modern sporting rifle in general. Your summary should be conversational and provide a broad overview; you don't need to mention every designer or include specific dates. However, be sure you discuss the timeframe of major developments, for example you might say "in the 1950s, ArmaLite developed the AR-10 based on technology used in the Johnson light machinegun and...".