CNC machined hop chamber for M249 machine guns is made of a single piece of aluminium alloy with a red anodized finish. The hop chamber is compatible with the M249 series by manufactures A&K, PJ, Classic Army, Echo 1 and Matrix. Optimal nozzle lenght is 21 - 21,5mm. The nozzle from the packing also fit on standard (not NBU) cylinder heads. The hop chamber is fully compatible with the stock plastic nozzle.