Precision 6.01mm precision barrels from PDI are extremely precise (laser cut) with high tolerances of 0.002 mm accuracy. There is absolutely no other barrel that reaches such preciseness in the airsoft market. Stainless steel construction is superior to aluminum or brass barrels and reduces flex from vibration of full auto high impact firing. These are for serious tuners who want the most out of their guns. Note that due to the absolute accuracy and high tightness, precision BB's is recommended. When used with precision BBs, will increase firepower and accuracy of your MP7 by approx 5% - 10%.