Those looking for inner barrels can check these new arrivals at Nashville Airsoft. Thye range from 6.03 to 6.01... "Just in at Nashville Airsoft is a shipment of precision tightbore barrels from Bravo and Madbull. The Bravo is a 6.03mm I.D. steel barrel that has both the regular AEG and TM M14 hop up cuts. The Madbull is a 6.01 mm I.D. barrel made of 7075 aircraft alloy and also has the regular AEG and TM M14 hop up cuts."