Tech Data Please

[01gunsmith]

Hello, finished my 300 whisper in dpms upper ,hart 1-8 BBL, adjustable gas tube underneath a slotted free floating handgaurd, gas block is also hidden under gaurd. advanced armament supperssor oon a 20" BBl.
I am currently having problem getting the bolt to fully cycle and pick up another round. When my gas tube is completly open i still get good extraction and ejection but not quite enough to clear the back of the next bullet and pick it up.
Since most of this build was done at my shop i used the only resources i had for info [didnt know about this forum]
I need more pressure and i need the proper gas hole diameter in the BBL i have it at .70 thousanths at this point . my gas tube is 8" long.
What input can you guys give me. Do i need to open up the gas hole to a larger diameter on the BBL? is my tube too long for sub-sonic?
all replys appreciated