I recently purchased a G&G m4 gbb v2 with some upgraded parts, a mad bull 6.01 650mm tight bore and a 20'' outer barrel with a mock suppressor. All parts are brand new from the factory, including the gun. Unfortunately i didn't test fire the gun before i upgraded the parts, however afterwords i loaded up a mag and put it in the gun. When i tried to shoot the gun was cycling and shooting the gas but no bbs. I figured it was a feeding issue, one of which is very common as seen here https://www.youtube.com/watch?v=2eYHR4_7RkI
. After I moved the bucking back from blocking the bbs and put the inner barrel and hopup unit back (yes I lined everything up). Again I tried to fire, only this time It was feeding most bbs with the occasional double fire, but the fps was extremely low, traveled ~60 feet before the bb dips down or curves to the right. Ive tried turning the hopup up and down with little to no affect. Im kinda giving up hope for this gun, maybe I just need a new hop up system? Gas from the magazine going into the system is functioning perfectly but somewhere along the line its not getting behind the bb.