Echo 1 Has been bringing a lot of new replicas to the table. One that stands out is the AR 57 or Five Seven.
This new replica is based on an M4 platform with a converted upper receiver that allows for the use of P-90 type magazines. It is said it will accept low, mid and high capacity magazines. The upper receiver is one piece with the Ris rail making it very solid. Although by using the magazine on the top it eliminated the top rail users will still have both sides and the lower rail mounting points.