Introduced in 1960, all model 500s are based on the same basic concept designed by Carl Benson. Originally using a single action bar, that was known to bind and even break, this was changed to dual action bars in 1970, following the expiration of Remington's patent on the double action bar design. A single large locking lug is used to secure the breech. The magazine tube is located below the barrel, and is screwed into the receiver. The slide release is located to the left rear of the trigger guard, and the safety is located on the upper rear of the receiver (often called a "tang safety").