This particular rifle features a semi-automatic direct gas impingement system. Additionally this DI gun features a non adjustable mid-length gas system for those who need reliability over customization. Additionally you will notice that the this rifle features a Mil-spec style upper/lower receiver the 16.5" match-grade nitride heat treated Puritan barrel and a 14.5" M-LOK compatible free float hand guard. The POF USA is the battle ready rifle which is ready in just a moment's notice.