This gun appears to be "post" Pro-Line becasuse of the foregrip. I have a Pro-Line and I have to change springs for my velocity adjustment. All the foregrips I've seen like that have a hole for an allen key to adjust the velocity.
I agree with grimace on the threading, I have both a Sterling Threaded Barrel and a Spyder Threaded Barrel and it is definatly a Sterling Thread.
That Hopper appears to be an old generation VL as well.
Good luck hellion360.